# Astronauts who landed on the moon

Astronauts who landed on the moon during the Apollo 15, 16 and 17 missions brought back a large collection of rocks to the earth. Knowing the rocks weighed 139 lb when they were on the moon, determine (a) the weight of the rocks on the earth, (b) the mass of the rocks in slugs. The acceleration due to gravity on the moon is 5.30 ft/$s^2$.

#### Solution:

a) Use the following equation (Newton’s second law):

$W=mg$

(Where $W$ is weight, $m$ is mass, and $g$ is the acceleration of gravity)

$W=mg$

$139=m(5.3)$

$m=26.22 \,\text{lb}\cdot \text{s}^2/\text{ft}$

Now apply Newton’s second again, this time, the acceleration of gravity is 32.2 ft/$s^2$ on earth.

$W=(26.22)(32.2)$

$W=844.28$ lbs

b)

A slug is equal to $1 \,\text{lb}\cdot \text{s}^2/\text{ft}$. Thus, the rocks were 26.22 slugs.

a) $W=844.28$ lbs