Chapter 5: Projectile Motion Conceptual Physics – Flashcards
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distinguish between vector vs scalar quantities
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A vector has a magnitude and direction, while a scalar only has magnitude.
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Describe the components of projectile motion.
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The horizontal component of projectile motion is like the motion of a ball rolling freely along a level surface without friction or gravity.
The vertical component is like the motion of a freely falling object.
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Describe the downward motion of a horizontally launched projectile.
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The downward motion of a horizontally launched projectile is the same as that of free fall.
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At the instant a horizontally pointed cannon is fired, a cannonball is released and dropped to the ground. Which cannonball hits the ground first?
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They hit at the same time
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define trajectory
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a projectile's path
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How is the horizontal component of motion affected by the vertical component of motion?
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It is NOT! The horizontal and vertical components are independent of each other.
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How long does the "force of the thrower" act on a ball tossed into the air?
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The force exists only while the hand and ball are in contact. Once the ball is released, that propelling force is no more.
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True or false? At the top of its trajectory (highest point), the velocity of a projectile is always momentarily zero.
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FALSE. The horizontal velocity of a projectile does not change, so if a projectile has horizontal velocity it will have the same horizontal velocity at the top of its trajectory.
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At what point in its path does a projectile have minimum speed?
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At the top of its path. If launched vertically, it's speed at the top is zero. If launched at an angle, the vertical component of velocity is zero, and the horizontal velocity is the d=same as when it was launched.
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How fast would an airplane travel if its velocity is 80 km/hr and it is flying with a tailwind that is 20 km/hr?
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100 km/hr
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How fast would an airplane travel if its velocity is 80 km/hr and it is flying against the wind which has a velocity of 20 km/hr?
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60 km/hr
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How fast will a boat that normally travels 10 km/hr in still water be moving with respect to land if it sails directly across a stream that flows 10 km/hr?
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14.14 km/hr
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What is the resultant of two perpendicular vectors?
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The resultant is the diagonal of a rectangle constructed with the two vectors as sides
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How do components of vectors affect each other?
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The perpendicular components of a vector are independent of each other
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When a ball rolls along a horizontal surface, why is its velocity constant (acceleration = 0)
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No component of gravitational force acts horizontally
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component vector
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one of the vectors whose sum is the resultant vector
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projectile
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an object that moves through air or through space, acted on by only gravity
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resultant vector
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result of adding two or more vectors
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satellite
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An object that revolves around another object
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scalar quantity
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quantity with magnitude only
(speed, temperature, mass)
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vector quantity
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quantity with both magnitude and direction
(velocity, force, acceleration)
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magnitude
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a number (amount)
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gravity
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force of attraction between two objects
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vector
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an arrow
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Pythagorean Theorum
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A^2+B^2 = C^2
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True or False: the perpendicular are independent of each other
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True. It is the combined effects of the horizontal and vertical components the curved path of a projectile
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Is the downward motion of a horizontally projected object falling slower or the same as an object in free fall?
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a freely falling object and a horizontally projected object, in equal time both objects fall the same distance
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True or false, when an object is launched at an angle, the vertical distance of fall for any given angle
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True
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With NO gravity, what path does a projectile follow? How does this differ in the presence of gravity?
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a straight line path; and in the presence of gravity, the object falls beneath this line the same vertical distance per second as it would if released from rest.
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A projectile is launched at an angle into the air. Neglecting air resistance, what is the vertical acceleration? Horizontal acceleration?
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-10 m/s2; zero.
acceleration is change in velocity and/or direction
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Given the velocity of a projectile (neglecting air resistance), describe changes in the horizontal and vertical components along the path.
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Horizontal components do not change, vertical components do.
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Describe how far a projectile goes in equal time intervals.
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Because there is no horizontal acceleration, a projectile moves equal horizontal distances in equal time intervals.
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What is the shape of a projectile's path?
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A parabolic path
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At the top of a projectile's path, what is the vertical and horizontal velocity?
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Zero for vertical velocity; for horizontal velocity it is equal to the horizontal component of the initial velocity and all other points along the path.
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When fired at the same speed, the path for a projectile fired at a steep angle has a vertical component of velocity that is greater than, equal to, or less than when the projection angle is less? What about the range? What about hang-time?
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Greater than. The range is less, unless the sum of the two angles equals 90 degrees, then the range is the same. The hang time for the smaller angle is less.
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When projectiles are shot at the same speed but at different angles, they travel different or equal horizontal distances?
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Different distances, or ranges.
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At what angle can a maximum range usually be obtained?
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45 degrees.
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True or false, launch speed is reduced by an object's mass.
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True, note example of heavy javelin whose launch speed is reduced when thown upward due to its mass.
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Hang time: is the time airborne dependent on horizontal speed?
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No, because only the vertical component of velocity determines hang time. However, a running jump can increase the vertical component compared to a standing jump.
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At what point in its path does a projectile have minimum speed?
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At the top of the parabola where there is only the horizontal component of velocity.
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What is the effect of air resistance on a projectile?
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The path of the object falls below the idealized parabola.
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Why does a projectile raise to its maximum height in the same time that it takes for it to fall from that height?
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The deceleration (negative acceleration) going up is equal to the acceleration due to gravity going down.
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Does a projectile hit the ground with greater speed than it had when it was launched?
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No, it hits with the same speed.
