Question

By applying a 12-newton horizontal force, a 7-kilogram block is moved 12 meters in 3 seconds on a frictionless, horizontal surface. How much power was used in moving the block.
A) 144 watts
B)112 watts
C) 16 watts
D) 48 watts

Answer 1

If a 12-N force is applied continuously through a distance
of 12m, then the amount of work done is

           (force) x (distance) = (12 N) x (12 m)  =  144 joules.

Power = (work done) / (time to do the work)

           =     (144 joules) / (3 sec) =  48 joules/sec = 48 watts. 

We don't care what purpose the force was used for,
or how much friction was involved.