A factory worker pushes a crate of mass 28.7kg a distance of 4.70m along a level

Question

A factory worker pushes a crate of mass 28.7kg a distance of 4.70m along a level floor at constant velocity by pushing horizontally on it. The coefficient of kinetic friction between the crate and floor is 0.24.

Part A

What magnitude of force must the worker apply?

Part B

How much work is done on the crate by this force?

Part C

How much work is done on the crate by friction?

Part D

How much work is done by the normal force?

Part E

How much work is done by gravity?

Part F

What is the total work done on the crate?

Explanation / Answer

a) since constant velocity a = 0

F - friction = 0

F = friction = u m g = 0.24*28.6*9.81= 67.3 N

b) W = F d = 67.3*4.7= 316.3 J

c) W friction = - um g d = -316.3 J

d) W normal = N d cos theta
where theta is angle between N and motion = 90
cos 90 = 0

so W normal = 0

e) once again theta = 90

so W gravity = 0

f) W total = 316.3 - 316.3 + 0 + 0 = 0

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