Question

A box weighing 8.0 kg has to be moved from the floor to the back of the truck, using a ramp 2.5 m long inclined at 30°. The worker gives the box a push so that it has initial velocity of 5.0 m/s. Unfortunately, the friction is more than he estimated and the box stops 1.6 m up the ramp and slides back down.

a) Assuming the friction force is constant. find its magnitude.
b) How fast is the box moving when it reaches the bottom of the ramp?

Answer 1

a. Wb = m*g = 8kg * 9.8N/kg = 78.4 N. = Wt of block.

Epmax = mg*h-Fk*d
Epmax = 78.4*1.6*sin30 - Fk*1.6
Epmax = 62.72 - Fk*1.6

Ek = 62.72 - Ff*1.6
0.5m*V^2 = 62.72 - Ff*1.6
4*5^2 = 62.72 - Fk*1.6
100 = 62.72 - Ff*1.6
Ff*1.6 = 62.72-100 = -37.28
Ff = -23.3 N. = Force of friction

b V = Vo = 5 m/s^2.