Exercício de Dinamica Aplicada (137)

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298 
 
PROBLEM 12.1 
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/s2. 
 
SOLUTION 
Since the rocks weighed 139 lb on the moon, their mass is 
 2moon
2
moon
139 lb
26.226 lb s /ft
5.30 ft/s
W
m
g
= = = ⋅ 
(a) On the earth, earth earthW mg= 
 2 2(26.226 lb s /ft)(32.2 ft/s )w = ⋅ 844 lbw =  
(b) Since 21 slug 1 lb s /ft,= ⋅ 26.2 slugsm = 