Power in physics terms depends on both work and time because of the equation P=W/T
Hope this helps :D
Explanation:
Given that,
Mass of the shopping cart, 
Initial speed of the shopping cart, 
Mass of the box, 
Initial speed of the box,
(at rest)
They stick together and continue moving at a new velocity. It is a case of inelastic collision.
(a) The momentum of the shopping cart before the collision is given by :

(b) The momentum of the box before the collision is given by :

(c) The velocity of the combined shopping cart/box wreckage after the collision is given by using the conservation of momentum as :

Hence, this is the required solution.
Resistance in wires causes thermal energy. The correct
answer between all the choices given is the third choice or letter C. I am
hoping that this answer has satisfied your query and it will be able to help
you in your endeavor, and if you would like, feel free to ask another question.