Question dealing with Objects in Motion?

Question

A dockworker applies a constant horizontal force of 75.0 N to a block of ice on a smooth horizontal floor. The frictional force is negligible. The block starts from rest and moves 16.0 m in 6.00 s
.
(a) What is the mass of the block of ice?


(b) If the worker stops pushing after 6.00 s, how far does the block move in the next 6.00 s?

Answer 1

Lets solve for the speed of the block at the 6 second point using conservation of energy
75*16=.5*m*v^2
m=2*75*16/v^2
m=2400/v^2

since f=m*a
75=m*a
a=75/m
and v(t)=a*t
v(6)=75*6/m
v^2=75^2*36/m^2
substituting from above

m=2400*m^2/(75^2*36)
m=(75^2*36)/2400
=84.38 kg

and v(6)=16/3 m/s

so in 6 seconds the block will move
16*2, or 32 meters

j