Question

A 100 N box falls from a truck moving at 25 m/s and slides to a stop in 55 m. What is the coefficient of friction between the box and the highway? How much work was done on the box by friction?

Answer 1

The only force acting on the box while it slides to a stop is kinetic friction which is equal to \[\mu _{k} N = \mu _{k} mg\] This force gives rise to the acceleration which is negative since the box is slowing down. We can find the value of the acceleration from\[v _{f}^{2} =v _{i}^2 + 2a \Delta x\] and use Newton's 2nd to set up a solution for the coefficient\[\mu _{k} mg = ma\] Solve for the coefficient.

To get the work, \[W = \Delta K = \mu _{k} mg * \Delta x\] Where K is the kinetic energy

Answer 2

Note that the work will come out to be negative

Answer 3

Oh okay I think I got the right answer now. Thank-you very much ^_^