A toy chest and its contents have a combined weight of 180 N. The coefficient of

Question

A toy chest and its contents have a combined weight of 180 N. The coefficient of static friction between toy chest and floor is 0.42. The child in Fig. 6-35 attempts to move the chest across the floor by pulling on an attached rope.

a. Calcualte the coefficient of kinetic friction betwee the chest and floor.

b. Calcualte the normal force during this motion.

c. Calculate the work done by the child for this motion.

d. Calculate the work done by the normal force for this motion.

e. Calculate the work done by the friction for this motion.

f. What is the net work done for this motion?

Explanation / Answer

a] Let it be u..

Balancing force in horizontal as velocity is constant

F cos theta = uN

55 cos 22.8 degree = u*(180- 55 sin 22.8 degree)

50.7 = 158.7 u

u = 50.7/158.7

= 0.32

b] N = 158.7 N

c] work done by child = Fd cos theta

= 50.7*6

= 304.2 J

d] work done by normal = 0 Work done by normal will be zero as it is perpendicular to motion,

E] work done by friction = -50.7*6 = -304.2 J   friction force is opposite to displacement, so there is negative sign, magnitude is same as applied pull in horizontal for balancing it.

F] Net work done = 304.2-304.2 = 0 J

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