Find work done on a sled by the force, gravity and friction.

Question

A horizontal force is used to push a 6 kg sled at constant speed 4 m up a 30 degree incline. If the kinetic coefficient is 0.2, find the work done on the sled by :

a) the force (answer: 179 J)

b) the gravity force (answer: -118 J )

c) the friction force (answer: -61.4 J)

Answer 1

Constant speed ==> a = 0 hence ∑F = 0 ( results may vary if g = 10 taken )

F = Weight Component + Friction = mgsin30 + mgcos30 x 0.2 = (6 x 9.8 x 0.5) + ( 6 x 9.8 x 0.87 x 0.2) = 29.4 +10.2 = 39.6N

a) W_(F) = 39.6 x 4 = +159.4J

b) mgsin30 x 4 = 6 x -9.8 x 0.5 x 4 = -117.6J

c) Friction x L = 10.2 x 4 = -40.8J

These may help.