A student wants to determine the coefficients of static friction and kinetic friction between a box and a plank. She places the box on the plank and gradually raises one end of the plank. When the angle of inclination with the horizontal reaches 30°, the box starts to slip, and it slides 2.4 m down the plank in 3.6 s at constant acceleration.

Question

A student wants to determine the coefficients of static friction and kinetic friction between a box and a plank. She places the box on the plank and gradually raises one end of the plank. When the angle of inclination with the horizontal reaches 30°, the box starts to slip, and it slides 2.4 m down the plank in 3.6 s at constant acceleration. 
(a) What is the coefficient of static friction?

(b) What is the coefficient of kinetic friction?

drwls · Answer

a) tan 30
b) write the equation of motion, with a retarding force proportional to the kinetic friction coefficient, Uk. Compute the acceleration from the fact it takes 3.6 s to make it down the plank, starting at zero velocity. Solve for Uk

john · Answer

During an Olympic bobsled run, the Jamaican team makes a turn of radius 7.6 m at a speed of 97.2 km/h. What is their accelaration in g?