A trunk with a weight of 210 N rests on the floor. The coefficient of static fri

Question

A trunk with a weight of 210 N rests on the floor. The coefficient of static friction between the trunk and the floor is 0.40, and the coefficient of kinetic friction is 0.29. (a) What is the magnitude of the minimum horizontal force with which a person must push on the trunk to start it moving? (b) Once the trunk is moving, what magnitude of horizontal force must the person apply to keep it moving with constant velocity? (c) If the person continued to push with the force used to start the motion, what would be the magnitude of the trunk's acceleration?

Explanation / Answer

here,

weight , w = 210 N

us = 0.4

uk = 0.29

mass , m = w/g

m = 210/9.8

m = 21.43 kg

(a)

let the magnitude of the minimum horizontal force with which a person must push on the trunk to start it moving be f

f = us * w

f = 0.4 * 210

f = 84 N

magnitude of the minimum horizontal force with which a person must push on the trunk to start it moving is 84 N

(b)

the magnitude of horizontal force must the person apply to keep it moving with constant velocity be f'

f' = uk * w

f' = 0.29 * 210

f' = 60.9 N

magnitude of horizontal force must the person apply to keep it moving with constant velocity is 60.9 N

(c)

let the accelration be a

f - f' = m * a

84 - 60.9 = 21.43 * a

a = 1.08 m/s^2

the accelration is 1.08 m/s^2

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