A person uses a rope to pull on a box across a rough surface. He exerts a force

Question

A person uses a rope to pull on a box across a rough surface. He exerts a force of 240 N while friction exerts a force of 180 N in the opposite direction. The box has a mass of 100 kg.

A.) The person reduces to the tension but continues to pull the box along at a constant speed for another 3.0 s. What force is the person putting on the box to keep it moving?

B.)The person gets tired after 3.0 s and reduces the tension in the rope to just 80 N. the friction force remains the same. What is the acceleration of the box and how long does it take to come to rest?

Explanation / Answer

a)

180 N

b)

a = (180-80)/100 = 1 m/s2

v = ((240-180)/100) * 3 = 1.8 m/s

t = v/a = 1.8/1 = 1.8 s

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