A 3 kg block is sliding across a horizontal surface. The initial speed of the bl

Question

A 3 kg block is sliding across a horizontal surface. The initial speed of the block is 4 m/s, but because of friction the block’s speed will decrease at a constant rate (i.e., constant acceleration) until the block finally comes to a stop after sliding 8 m. What is the average power (in W) supplied by friction as the block slows to a stop?

A 3 kg block is sliding across a horizontal surface. The initial speed of the block is 4 m/s, but because of friction the block’s speed will decrease at a constant rate (i.e., constant acceleration) until the block finally comes to a stop after sliding 8 m. What is the average power (in W) supplied by friction as the block slows to a stop?

Explanation / Answer

apply equation of motion,

v^2 - u^2 = 2*a*s

0 - 4^2 = 2*a*8

a = -1 m/s^2

let time taken by block to stop,

Vf - Vi = a*t

0 - 4 = -1*t

t = 4 sec

now ppower is given by

Power = KE / time

P = 0.5*m*v2 / t

P = 0.5*3*42 / 4

P = 6 W

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