Work done by force of gravity?

Question

Work done by the force of gravity?

starting from rest a 7.0 kg block slides 2.4 m down a rough 35 degree incline in 2.0 s.... the acceleration of gravity is 9.81m/s2 find the work done by the force of gravity?.... answer in J

also find the change in mechanical energy due to friction...answer in J

also find the work done by the normal force between the block and the incline. answer in units J.

Answer 1

Vertical drop=2.4sin35=1.3765m

Work done by gravity=1.3765x9.81x7=94.52 J

Wihout friction acceleration=9.81sin35=5.162m/sec^2

In your case assuming uniform acceleration

2.4=(1/2)*a*2^2 or acceleration=1.2m/sec^2

Frictional force=7(5.162-1,2)=27.73 Newtons

Frictional energy=27.73x2.4=66.564 J

Normal Force=7.0X9.81Xsin35=39.38 Newtons(From the free body diagram)