Question

Consider the situation of the previous question from a frame moving with a speed v0 parallel to the initial velocity of the block. (a) What are the initial and final kinetic energies? (b) What is the work done by the kinetic friction?

Answer 1

Explanation:

According to the situation of the previous question from a frame moving with a speed $v_0$ parallel to the initial velocity of the block

(a) In this moving frame initial velocity will be zero,  

so initial kinetic energy  = 0

Final velocity = $-v_0$

So final K.E. = $\begin{equation}=\frac{1}{2} m v_{0}^{2}$

(b) Forces on the ball are weight, ordinary power and dynamic erosion. Since weight and typical power are equivalent and inverse, the resultant power on the ball is equivalent to active grinding. Work done by the resultant power is equivalent to change in dynamic vitality, so work done by active grating

= final kinetic energy - Initial Kinetic energy of the ball  

$\begin{equation}=\frac{m v_{0}^{2}}{2}-0=\frac{m v_{0}^{2}}{2}$