A rocket-propelled sled of mass 450 kg starts from rest and travels along a straight
PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A rocket-propelled sled of mass 450 kg starts from rest and travels along a straight, level track. A constant thrust force of 3.8 kN is produced by the rocket for 6.0 s. During this time the sled experiences a kinetic friction force of 650 N opposite its direction of motion. Assume the thrust remains directed horizontally and the mass of the sled is constant.
(a) Determine the work done by the rocket thrust on the sled during the 6.0 s interval.
(b) Calculate the work done by the kinetic friction force over the same interval.
(c) Using your answers to parts (a) and (b), compute the net change in the sled’s mechanical energy during the firing interval.
(d) Determine the average power actually delivered by the rocket engine to the sled (that is, the rate at which the engine does work on the sled) during the 6.0 s interval.
(e) Compare the average engine power found in part (d) with the average rate at which the sled’s kinetic energy increases, and explain the physical significance of any difference.