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At the instant a truck is travelling along a level pavement at 20 m/s, a wooden crate falls from the truck.
If the crate travels 40 meters before coming to rest, what is the coefficient of kinetic friction between
the crate and the road?
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In this Physics problem, we are given that a wooden crate slides along the level pavement,
having the initial speed of 20 m/s, and stops after traveling 40 meters.
The simplest way to solve the problem is to apply the Law of Conservation mechanical energy.
From one side, we have the kinetic energy of the sliding crate,
where "m" is its mass and "v" is its initial speed.
From the other side, we have the work of the friction force F*d, where F is the friction force k*(m*g),
k is the kinematic friction coefficient, g is the gravity acceleration and "d" is the the breaking distance (given).
The Conservation Law of mechanical energy allows us to write this equation
= k*m*g*d.
First, we cancel the mass in both sides and then we get the formula for the friction coefficient
k = = = = 0.5.
ANSWER. Under given conditions, the kinematic friction coefficient is 0.5.
Solved.