Question

A book is launched up along the rough incline. Kinetic energy given to a book at initial point is 100 J. Book comes to stop at some point having potential energy 80 J, after what book starts to slide back. What will be its kinetic energy when it will return to the initial launching point?
(A) 60 J
(B) 100 J
(C) 80J
(D) 180 J

Answer 1

Answer:

(A) 60 J

Explanation:

At state 1

KE₁=100 J

At state 2

KE₂ = 0

U₂=80 J

Given that surface is rough so friction force will act in opposite to the direction of motion

Lets take work done by friction = Wfr

From work power energy

Work done by all forces = Change in kinetic energy

Wfr + U₂=ΔKE

Wfr+80 = 100

Wfr= 20 J

Now when book slides from top position then

Wfr+ U = KEf - KEi

-20 + 80 = KEf-0

KEf= 60 J

(A) 60 J