6.32 A 50000-kg freight car is pulled 800 m up along a 1.20 percent grade at constant speed. (a) Find the work done against gravity by the drawbar pull. (b) If the friction force retarding the motion is 1500 N, find the total work done. Ans. (a) 4.70 MJ; (b) 5.90 MJ
6.32 A 50000-kg freight car is pulled 800 m up along a 1.20 percent grade at constant speed. (a) Find the work done against gravity by the drawbar pull. (b) If the friction force retarding the motion is 1500 N, find the total work done. Ans. (a) 4.70 MJ; (b) 5.90 MJ
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Transcribed Image Text:A 50 000-kg freight car is pulled 800 m up along a 1.20 percent grade at constant speed. (a) Find the work
done against gravity by the drawbar pull. (b) If the friction force retarding the motion is 1500 N, find the
6.32
total work done.
Ans. (a) 4.70 MJ; (b) 5.90 MJ
Given
Required
m = 50000 kg
W = ?
%3D
d = 800 m
F, = 1500 N
grade = 1.20 %
Solution
( a ) Find the work done against gravity by the drawbar pull 3
()
e = tan
1.2
W - mgh
W = (50000 kg) (O.8 m/s') ( 9.6 m)
100
0.6875°
%3D
h - s x sin ( 0.6875 )
= 470400 J I(4.70 mJ
%3D
h - 800 х sin ( 0,6875
h = 9,59 m
( b ) f the friction force retarding the motion is 1500 N. find the total
work done
W - F x d
W = 1500 N x 800 m
- 120000 J I 1.2 mJ
Wi- Wg+ Wr
%3D
W = 4.70 mJ + 1.2 mJ
5.90 mJ
%3D
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