A child is sitting on a stationary skateboard with a pile of

A child is sitting on a stationary skateboard with a pile of rocks which she throws in one direction in order to make the skateboard travel in the opposite direction. If the rocks each have a mass of 0.45 kg and she can throw them with a speed of 12 m/s relative to the ground, determine the number of rocks she must throw per minute in order to maintain a constant average speed against a 2.0 N force of friction. (Note: because this is a rate, the answer may not be a whole number.)
___ rocks/min

Solution

1 rocks/min