An Object of mass 7 kg is pushed along a surface up to a velocity of + 10 m/s before it is let go. It then slows to a stop due to an 11-N frictional force. How long until it comes to a stop?

initial KE=1/2 m vi^2

friction energy=force*distance
set these equal, and solve for distance.

then time:
time=distance/avgveloctiy=distance/10/2