Question

A block of mass 4 kg is placed gently on a conveyor belt moving at a constant speed of 5 m/s at t = 0. Coefficient of friction between the belt and the block is $\mu$ = 0.2. Power of friction force on block at t = 3 sec from ground frame of reference is $[g=10m/s^2]$(Write until two digits after the decimal point.)

Answer 1

$f_k=\mu N=\mu mg$
$a=\frac{f_k}{m}=\mu g$
Friction acts on the block till the block achieves 5 m/s.
$a=\mu g=0.2\times 10=2m/s$
$v=u+at\Rightarrow 5=0+2\times t\Rightarrow t=2.5sec$
Therefore, friction only acts until 2.5 sec.
So, at t = 3 sec, friction = 0.
Hence, the power delivered is zero.