Question

An observer and a vehicle, both start moving together from rest (towards right) with acceleration 5 $m/s^2$ and 2 $m/s^2$, respectively. There is a $1kg$ block on the floor of the vehicle and coefficient of friction is $\mu =0.3$ between their surface. Friction force observed by the observer is $2N$. What is the magnitude of the work done (in J) by frictional force on the $1kg$ block observed by the running observer, during first second of the motion.

Answer 1

The frictional force as observed by observer is $2N$, as block is accelerating with acceleration of $2m/s^2$.

As the observer is moving with an acceleration of $5m/s^2$ we get the acceleration of the block w.r.t the observer as $3m/s^2$

Thus, its displacement in first second is given as $s=\frac{1}{2}a{t}^2=1.5m$
Thus, we get the work done by the frictional force as $2\times 1.5=3J$