Physics
Physics
1st Edition
Walker
ISBN: 9780133256925
Textbook solutions

All Solutions

Page 317: Practice Problems

Exercise 18
Step 1
1 of 3
$textbf{Given: }$

The mass of the lunar rover on the Apollo missions is $m = 225 mathrm{~kg}$.

$textbf{Required: }$

Finding the weight of the lunar rover on the Apollo missions on Earth and on the Moon.

Step 2
2 of 3
$textbf{Calculation: }$

Solve for the weight of the lunar rover on the Apollo missions on Earth:

In order to evaluate the weight of the lunar rover on the Apollo missions, we use the following relation:

$$
begin{align*}
W_{E} &= m ~ a_{E} \
&= 225 mathrm{~kg} times 9.8 mathrm{~m/s^{2}} \
&= 2205 mathrm{~N}
end{align*}
$$

So, the weight of the lunar rover on the Apollo missions on Earth is $2205 mathrm{~N}$.

Solve for the weight of the lunar rover on the Apollo missions on Moon:

As we know the accerlation due to the gravity on the Moon is $1.62 mathrm{~m/s^{2}}$. In order to evaluate the weight of the lunar rover on the Apollo missions, we use the following relation:

$$
begin{align*}
W_{M} &= m ~ a_{M} \
&= 225 mathrm{~kg} times 1.62 mathrm{~m/s^{2}} \
&= 364.5 mathrm{~N}
end{align*}
$$

So, the weight of the lunar rover on the Apollo missions on Moon is $364.5 mathrm{~N}$.

Result
3 of 3
The weight of the lunar rover on the Apollo missions on Earth is $2205 mathrm{~N}$.

The weight of the lunar rover on the Apollo missions on Moon is $364.5 mathrm{~N}$.

Exercise 19
Step 1
1 of 4
$textbf{Given: }$

The mass of the object is $m_{1} = 4.6 mathrm{~kg}$. The mass of Earth is $m_{2} = 5.97 times 10^{24} mathrm{~kg}$. The gravitational force between the object and the Earth is $F = 2.2 mathrm{~N}$.

$textbf{Required: }$

(a) Finding the distance between the object and the Earth.

(b) Finding the initial acceleration of the object.

Step 2
2 of 4
(a) $textbf{Calculation: }$

As Newton’s law of universal gravitation, The force of gravity between two objects is given by

$$
begin{align*}
F &= G ~ dfrac{ m_{1} ~ m_{2} }{ r^{2} }
end{align*}
$$

Rearrange and solve for the distance between the object and the Earth:

$$
begin{align*}
r &= sqrt{ G ~ dfrac{ m_{1} ~ m_{2} }{ F} } \
&= sqrt{ 6.67 times 10^{-11} mathrm{~N cdot m^{2}/kg^{2}} ~ dfrac{ 4.6 mathrm{~kg} times 5.97 times 10^{24} mathrm{~kg} }{ 2.2 mathrm{~N} } } \
&= 2.885 times 10^{7} mathrm{~m}
end{align*}
$$

So, the distance between the object and the Earth is $2.885 times 10^{7} mathrm{~m}$.

Step 3
3 of 4
(b) $textbf{Calculation: }$

According to Newton’s second law:

$$
begin{align*}
sum F &= m ~ a \
end{align*}
$$

Rearrange and solve for the initial acceleration of the object:

$$
begin{align*}
a &= dfrac{ F}{m} \
&= dfrac{2.2 mathrm{~N} }{ 4.6 mathrm{~kg} } \
&= 0.478 mathrm{~m/s^{2}}
end{align*}
$$

So, the initial acceleration of the object is $0.478 mathrm{~m/s^{2}}$.

Result
4 of 4
(a) The distance between the object and the Earth is $2.885 times 10^{7} mathrm{~m}$.

(b) The initial acceleration of the object is $0.478 mathrm{~m/s^{2}}$.

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