Chapter 6 Physics – Flashcards

What is the correct unit of work expressed in SI units? A) kg m/s2 B) kg m2/s C) kg m2/s2 D) kg2 m/s2

Can work be done on a system if there is no motion? A) Yes, if an outside force is provided. B) Yes, since motion is only relative. C) No, since a system which is not moving has no energy. D) No, because of the way work is defined.

If you push twice as hard against a stationary brick wall, the amount of work you do A) doubles. B) is cut in half. C) remains constant but non-zero. D) remains constant at zero.

A 50-N object was lifted 2.0 m vertically and is being held there. How much work is being done in holding the box in this position? A) more than 100 J B) 100 J C) less than 100 J, but more than 0 J D) 0 J

If you walk 5.0 m horizontally forward at a constant velocity carrying a 10-N object, the amount of work you do is A) more than 50 J. B) equal to 50 J. C) less than 50 J, but more than 0 J. D) zero.

A container of water is lifted vertically 3.0 m then returned to its original position. If the total weight is 30 N, how much work was done? A) 45 J B) 90 J C) 180 J D) No work was done.

Does the centripetal force acting on an object do work on the object? A) Yes, since a force acts and the object moves, and work is force times distance. B) Yes, since it takes energy to turn an object. C) No, because the object has constant speed. D) No, because the force and the displacement of the object are perpendicular.

You throw a ball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down. A) Work is + on the way up and + on the way down. B) Work is + on the way up and - on the way down. C) Work is - on the way up and + on the way down. D) Work is - on the way up and - on the way down.

The area under the curve, on a Force versus position (F vs. x) graph, represents A) work. B) kinetic energy. C) power. D) potential energy.

On a plot of Force versus position (F vs. x), what represents the work done by the force F? A) the slope of the curve B) the length of the curve C) the area under the curve D) the product of the maximum force times the maximum x

The quantity 1/2 mv2 is A) the kinetic energy of the object. B) the potential energy of the object. C) the work done on the object by the force. D) the power supplied to the object by the force.

If the net work done on an object is positive, then the object's kinetic energy A) decreases. B) remains the same. C) increases. D) is zero.

If the net work done on an object is negative, then the object's kinetic energy A) decreases. B) remains the same. C) increases. D) is zero.

If the net work done on an object is zero, then the object's kinetic energy A) decreases. B) remains the same. C) increases. D) is zero.

A truck weighs twice as much as a car, and is moving at twice the speed of the car. Which statement is true about the truck's kinetic energy compared to that of the car? A) All that can be said is that the truck has more kinetic energy. B) The truck has twice the kinetic energy of the car. C) The truck has 4 times the kinetic energy of the car. D) The truck has 8 times the kinetic energy of the car.

Car J moves twice as fast as car K, and car J has half the mass of car K. The kinetic energy of car J, compared to car K is A) the same. B) 2 to 1. C) 4 to 1. D) 1 to 2.

An object hits a wall and bounces back with half of its original speed. What is the ratio of the final kinetic energy to the initial kinetic energy? A) 1/2 B) 1/4 C) 2 D) 4

A brick is moving at a speed of 3 m/s and a pebble is moving at a speed of 5 m/s. If both objects have the same kinetic energy, what is the ratio of the brick's mass to the rock's mass? A) 25 to 9 B) 5 to 3 C) 12.5 to 4.5 D) 3 to 5

A 4.0-kg mass is moving with speed 2.0 m/s. A 1.0-kg mass is moving with speed 4.0 m/s. Both objects encounter the same constant braking force, and are brought to rest. Which object travels the greater distance before stopping? A) the 4.0-kg mass B) the 1.0-kg mass C) Both travel the same distance. D) cannot be determined from the information given

You slam on the brakes of your car in a panic, and skid a certain distance on a straight, level road. If you had been traveling twice as fast, what distance would the car have skidded, under the same conditions? A) It would have skidded 4 times farther. B) It would have skidded twice as far. C) It would have skidded 1.4 times farther. D) It is impossible to tell from the information given.

A planet of constant mass orbits the Sun in an elliptical orbit. Neglecting any friction effects, what happens to the planet's kinetic energy? A) It remains constant. B) It increases continually. C) It decreases continually. D) It increases when the planet approaches the Sun, and decreases when it moves farther away.

The quantity mgy is A) the kinetic energy of the object. B) the gravitational potential energy of the object. C) the work done on the object by the force. D) the power supplied to the object by the force.

The quantity 1/2 kx2 is A) the kinetic energy of the object. B) the elastic potential energy of the object. C) the work done on the object by the force. D) the power supplied to the object by the force.

Is it possible for a system to have negative potential energy? A) Yes, as long as the total energy is positive. B) Yes, since the choice of the zero of potential energy is arbitrary. C) No, because the kinetic energy of a system must equal its potential energy. D) No, because this would have no physical meaning.

An object is released from rest a height h above the ground. A second object with four times the mass of the first if released from the same height. The potential energy of the second object compared to the first is A) one-fourth as much. B) one-half as much. C) twice as much. D) four times as much.

A 0.200-kg mass attached to the end of a spring causes it to stretch 5.0 cm. If another 0.200-kg mass is added to the spring, the potential energy of the spring will be A) the same. B) twice as much. C) 3 times as much. D) 4 times as much.

The total mechanical energy of a system A) is equally divided between kinetic energy and potential energy. B) is either all kinetic energy or all potential energy, at any one instant. C) can never be negative. D) is constant, only if conservative forces act.

An acorn falls from a tree. Compare its kinetic energy K, to its potential energy U. A) K increases and U decreases. B) K decreases and U decreases. C) K increases and U increases. D) K decreases and U increases.

Describe the energy of a car driving up a hill. A) entirely kinetic B) entirely potential C) both kinetic and potential D) gravitational

A lightweight object and a very heavy object are sliding with equal speeds along a level frictionless surface. They both slide up the same frictionless hill. Which rises to a greater height? A) The heavy object, because it has greater kinetic energy. B) The lightweight object, because it weighs less. C) They both slide to the same height. D) cannot be determined from the information given

Consider two masses m1 and m2 at the top of two frictionless inclined planes. Both masses start from rest at the same height. However, the plane on which m1 sits is at an angle of 30e with the horizontal, while the plane on which m2 sits is at 60e. If the masses are released, which is going faster at the bottom of its plane? A) m1 B) m2 C) They both are going the same speed. D) cannot be determined without knowing the masses

A ball falls from the top of a building, through the air (air friction is present), to the ground below. How does the kinetic energy (K) just before striking the ground compare to the potential energy (U) at the top of the building? A) K is equal to U. B) K is greater than U. C) K is less than U. D) It is impossible to tell.

A ball drops some distance and gains 30 J of kinetic energy. Do not ignore air resistance. How much gravitational potential energy did the ball lose? A) more than 30 J B) exactly 30 J C) less than 30 J D) cannot be determined from the information given

A ball drops some distance and loses 30 J of gravitational potential energy. Do not ignore air resistance. How much kinetic energy did the ball gain? A) more than 30 J B) exactly 30 J C) less than 30 J D) cannot be determined from the information given

The quantity Fd/t is A) the kinetic energy of the object. B) the potential energy of the object. C) the work done on the object by the force. D) the power supplied to the object by the force.

What is the correct unit of power expressed in SI units? A) kg m/s2 B) kg m2/s2 C) kg m2/s3 D) kg2 m/s2

Of the following, which is not a unit of power? A) watt/second B) newton-meter/second C) joule/second D) watt

Compared to yesterday, you did 3 times the work in one-third the time. To do so, your power output must have been A) the same as yesterday's power output. B) one-third of yesterday's power output. C) 3 times yesterday's power output. D) 9 times yesterday's power output.

To accelerate your car at a constant acceleration, the car's engine must A) maintain a constant power output. B) develop ever-decreasing power. C) develop ever-increasing power. D) maintain a constant turning speed.

An object is lifted vertically 2.0 m and held there. If the object weighs 90 N, how much work was done in lifting it? A) 360 J B) 180 J C) 90 J D) 0 J

You lift a 10-N physics book up in the air a distance of 1.0 m, at a constant velocity of 0.50 m/s. What is the work done by the weight of the book? A) +10 J B) -10 J C) +5.0 J D) -5.0 J

A 500-kg elevator is pulled upward with a constant force of 5500 N for a distance of 50.0 m. What is the work done by the 5500 N force? A) 2.75 ˛ 105 J B) -2.45 ˛ 105 J C) 3.00 ˛ 104 J D) -5.20 ˛ 105 J

A 500-kg elevator is pulled upward with a constant force of 5500 N for a distance of 50.0 m. What is the work done by the weight of the elevator? A) 2.75 ˛ 105 J B) -2.45 ˛ 105 J C) 3.00 ˛ 104 J D) -5.20 ˛ 105 J

A 500-kg elevator is pulled upward with a constant force of 5500 N for a distance of 50.0 m. What is the net work done on the elevator? A) 2.75 ˛ 105 J B) -2.45 ˛ 105 J C) 3.00 ˛ 104 J D) -5.20 ˛ 105 J

A 30-N box is pulled 6.0 m up along a 37e inclined plane. What is the work done by the weight (gravitational force) of the box? A) -11 J B) -1.1 ˛ 102J C) -1.4 ˛ 102 J D) -1.8 ˛ 102 J

A 4.00-kg box of fruit slides 8.0 m down a ramp, inclined at 30.0e from the horizontal. If the box slides at a constant velocity of 5.00 m/s, what is the work done by the weight of the box? A) 157 J B) -157 J + 78.4 J C) 78.4 J D) -78.4 J

Matthew pulls his little sister Sarah in a sled on an icy surface (assume no friction), with a force of 60.0 N at an angle of 37.0e upward from the horizontal. If he pulls her a distance of 12.0 m, what is the work done by Matthew? A) 185 J B) 433 J C) 575 J D) 720 J

A force moves an object in the direction of the force. The graph in Fig. 6-1 shows the force versus the object's position. Find the work done when the object moves from 0 to 2.0 m. A) 20 J B) 40 J C) 60 J D) 80 J

A force moves an object in the direction of the force. The graph in Fig. 6-1 shows the force versus the object's position. Find the work done when the object moves from 2.0 to 4.0 m. A) 20 J B) 40 J C) 60 J D) 80 J

A force moves an object in the direction of the force. The graph in Fig. 6-1 shows the force versus the object's position. Find the work done when the object moves from 4.0 to 6.0 m. A) 20 J B) 40 J C) 60 J D) 80 J

A force moves an object in the direction of the force. The graph in Fig. 6-1 shows the force versus the object's position. Find the work done when the object moves from 0 to 6.0 m. A) 20 J B) 40 J C) 60 J D) 80 J

A horizontal force of 200 N is applied to move a 55-kg cart (initially at rest) across a 10 m level surface. What is the final kinetic energy of the cart? A) 1.0 ˛ 103 J B) 2.0 ˛ 103 J C) 2.7 ˛ 103 J D) 4.0 ˛ 103 J

A horizontal force of 200 N is applied to move a 55-kg cart (initially at rest) across a 10 m level surface. What is the final speed of the cart? A) 73 m/s B) 36 m/s C) 8.5 m/s D) 6.0 m/s

A 10-kg mass is moving with a speed of 5.0 m/s. How much work is required to stop the mass? A) 50 J B) 75 J C) 100 J D) 125 J

If it takes 50 m to stop a car initially moving at 25 m/s, what distance is required to stop a car moving at 50 m/s under the same condition? A) 50 m B) 100 m C) 200 m D) 400 m

A spring-driven dart gun propels a 10-g dart. It is cocked by exerting a force of 20 N over a distance of 5.0 cm. With what speed will the dart leave the gun, assuming the spring has negligible mass? A) 10 m/s B) 14 m/s C) 17 m/s D) 20 m/s

A 100-N force has a horizontal component of 80 N and a vertical component of 60 N. The force is applied to a box which rests on a level frictionless floor. The cart starts from rest, and moves 2.0 m horizontally along the floor. What is the cart's final kinetic energy? A) 200 J B) 160 J C) 120 J D) zero

An arrow of mass 20 g is shot horizontally into a bale of hay, striking the hay with a velocity of 60 m/s. It penetrates a depth of 20 cm before stopping. What is the average stopping force acting on the arrow? A) 45 N B) 90 N C) 180 N D) 360 N

A 15.0-kg object is moved from a height of 7.00 m above a floor to a height of 13.0 m above the floor. What is the change in gravitational potential energy? A) zero B) 1030 J C) 1176 J D) 1910 J

A 400-N box is pushed up an inclined plane. The plane is 4.0 m long and rises 2.0 m. If the plane is frictionless, how much work was done by the push? A) 1600 J B) 800 J C) 400 J D) 100 J

A 10-kg mass, hung onto a spring, causes the spring to stretch 2.0 cm. What is the spring constant? A) 4.9 ˛ 103 N/m B) 5.0 ˛ 103 N/m C) 20 N/m D) 2.0 N/m

A spring is characterized by a spring constant of 60 N/m. How much potential energy does it store, when stretched by 1.0 cm? A) 3.0 ˛ 10-3 J B) 0.30 J C) 60 J D) 600 J

Calculate the work required to compress an initially uncompressed spring with a spring constant of 25 N/m by 10 cm. A) 0.10 J B) 0.13 J C) 0.17 J D) 0.25 J

What work is required to stretch a spring of spring constant 40 N/m from x = 0.20 m to 0.25 m? (Assume the unstretched position is at x = 0.) A) 0.45 J B) 0.80 J C) 1.3 J D) 0.050 J

A spring with a spring constant of 15 N/m is initially compressed by 3.0 cm. How much work is required to compress the spring an additional 4.0 cm? A) 0.0068 J B) 0.012 J C) 0.024 J D) 0.030 J

A 60-kg skier starts from rest from the top of a 50-m high slope. What is the speed of the slier on reaching the bottom of the slope? (Neglect friction.) A) 22 m/s B) 31 m/s C) 9.8 m/s D) 41 m/s

A skier, of mass 40 kg, pushes off the top of a hill with an initial speed of 4.0 m/s. Neglecting friction, how fast will she be moving after dropping 10 m in elevation? A) 7.3 m/s B) 15 m/s C) 49 m/s D) 196 m/s

An object slides down a frictionless inclined plane. At the bottom, it has a speed of 9.80 m/s. What is the vertical height of the plane? A) 19.6 m B) 9.80 m C) 4.90 m D) 2.45 m

A 1.0-kg ball falls to the floor. When it is 0.70 m above the floor, its potential energy exactly equals its kinetic energy. How fast is it moving? A) 3.7 m/s B) 6.9 m/s C) 14 m/s D) 45 m/s

A toy rocket, weighing 10 N, blasts straight up from ground level with a kinetic energy of 40 J. At the exact top of its trajectory, its total mechanical energy is 140 J. To what vertical height does it rise? A) 1.0 m B) 10 m C) 14 m D) 24 m

A projectile of mass m leaves the ground with a kinetic energy of 220 J. At the highest point in its trajectory, its kinetic energy is 120 J. To what vertical height, relative to its launch point, did it rise? A) 220/(mg) meters B) 120/(mg) meters C) 100/(mg) meters D) Impossible to determine without knowing the angle of launch

A roller coaster starts from rest at a point 45 m above the bottom of a dip (See Fig. 6-2). Neglect friction, what will be the speed of the roller coaster at the top of the next slope, which is 30 m above the bottom of the dip? A) 14 m/s B) 17 m/s C) 24 m/s D) 30 m/s

A roller coaster starts with a speed of 5.0 m/s at a point 45 m above the bottom of a dip (See Fig. 6-2). Neglect friction, what will be the speed of the roller coaster at the top of the next slope, which is 30 m above the bottom of the dip? A) 12 m/s B) 14 m/s C) 16 m/s D) 18 m/s

A roller coaster starts at a point 30 m above the bottom of a dip with a speed of 25 m/s (See Fig. 6-2). Neglect friction, what will be the speed of the roller coaster at the top of the next slope, which is 45 m above the bottom of the dip? A) 14 m/s B) 16 m/s C) 18 m/s D) 20 m/s

What is the minimum speed of the ball at the bottom of its swing (point B) in order for it to reach point A, which is 1.0-m above the bottom of the swing? FIGURE 6-3 A) 2.2 m/s B) 3.1 m/s C) 4.4 m/s D) 4.9 m/s

A pendulum of length 50 cm is pulled 30 cm away from the vertical axis and released from rest. What will be its speed at the bottom of its swing? A) 0.50 m/s B) 0.79 m/s C) 1.2 m/s D) 1.4 m/s

A 1500-kg car moving at 25 m/s hits an initially uncompressed horizontal spring with spring constant of 2.0 ˛ 106 N/m. What is the maximum compression of the spring? (Neglect the mass of the spring.) A) 0.17 m B) 0.34 m C) 0.51 m D) 0.68 m

A driver, traveling at 22 m/s, slows down her 2000 kg car to stop for a red light. What work is done by the friction force against the wheels? A) -2.2 ˛ 104 J B) -4.4 ˛ 104 J C) -4.84 ˛ 105 J D) -9.68 ˛ 105 J

The kinetic friction force between a 60.0-kg object and a horizontal surface is 50.0 N. If the initial speed of the object is 25.0 m/s, what distance will it slide before coming to a stop? A) 15.0 m B) 30.0 m C) 375 m D) 750 m

A 12-kg object is moving on a rough, level surface. It has 24 J of kinetic energy. The friction force on it is a constant 0.50 N. How far will it slide? A) 2.0 m B) 12 m C) 24 m D) 48 m

A force of 10 N is applied horizontally to a 2.0-kg mass on a level surface. The coefficient of kinetic friction between the mass and the surface is 0.20. If the mass is moved a distance of 10 m, what is the change in its kinetic energy? A) 20 J B) 39 J C) 46 J D) 61 J

A 60-kg skier starts from rest from the top of a 50-m high slope. If the work done by friction is -6.0 ˛ 103 J, what is the speed of the skier on reaching the bottom of the slope? A) 17 m/s B) 24 m/s C) 34 m/s D) 31 m/s

An 800-N box is pushed up an inclined plane. The plane is 4.0 m long and rises 2.0 m. It requires 3200 J of work to get the box to the top of the plane. What was the magnitude of the average friction force on the box? A) 0 N B) non-zero, but less than 400 N C) 400 N D) greater than 400 N

At what rate is a 60.0-kg boy using energy when he runs up a flight of stairs 10.0-m high, in 8.00 s? A) 75.0 W B) 735 W C) 4.80 kW D) 48 W

A 10-N force is needed to move an object with a constant velocity of 5.0 m/s. What power must be delivered to the object by the force? A) 0.50 W B) 1.0 W C) 50 W D) 100 W

How many joules of energy are used by a 1.0 hp motor that runs for 1.0 hr? (1 hp = 746 W) A) 3.6 ˛ 103 J B) 2.7 ˛ 106 J C) 4.5 ˛ 104 J D) 4.8 J

A cyclist does work at the rate of 500 W while riding. How much force does her foot push with when she is traveling at 8.0 m/s? A) 31 N B) 63 N C) 80 N D) 4000 N

A 1500-kg car accelerates from 0 to 25 m/s in 7.0 s. What is the average power delivered by the engine? (1 hp = 746 W) A) 60 hp B) 70 hp C) 80 hp D) 90 hp