A crate of mass 50 kg is being pushed across a rough surface at a steady 8.0 m/s. The crate is then released and comes to a stop in 10 seconds. What is the average rate at which the frictional force on the crate removes kinetic energy from it?
A boy throws a ball of mass 0.25 kg vertically upward with an initial speed of 20 m/s. The ball moves vertically upward, comes instantaneously to rest, and then accelerates vertically downward and returns to the point from which it was thrown. When the ball returns to its original position, its speed is 17 m/s. How much work was done by air resistance on the ball during its flight?
In a downhill ski race, surprisingly, little advantage is gained by getting a running start. This is because the initial kinetic energy is small compared with the gain in gravitational potential energy on even small hills.
Consider a skier who skies 80.0 m down a slope. Ignore any effects of friction.
Find the final speed if the skier starts at rest.
Find the time taken if the skier starts at rest.
Find the final speed if the skier starts with an initial speed of 2.50 m/s.
Find the time taken if the skier starts with an initial speed of 2.50 m/s.