Question

Consider two observers moving with respect to each other at a speed v along a straight line. They observe a bock of mass m moving a distance l on a rough surface. The following quantities will be same as observed by the two observers.
(a) kinetic energy of the block at time t
(b) work done by friction
(c) total work done on the block
(d) acceleration of the block.

Answer 1

(d) acceleration of the block

Acceleration of the block will be the same to both the observers. The respective kinetic energies of the observers are different, because the block appears to be moving with different velocities to both the observers. Work done by the friction and the total work done on the block are also different to the observers.