Concept #1: Power

Practice: A 350 g mass can undergo two different motions, propelled by gravity in each case: it can either fall a height of 10 cm, or it can slide down a frictionless incline at a 30° angle. In which case is the mass’ kinetic energy changing faster?

Air resistance at high speed is often given as Fair = bv2. If the terminal velocity of a 75 kg skydiver is 60 m/s, at what rate is the air resistance sapping the skydiver’s kinetic energy?

A car moves at a speed of 25 m/s. If the car were to experience 4.5 kN of air resistance at this speed, how much power would the engine need to produce to keep the car moving at a constant speed?

A 10 kg object slides along a surface with a coefficient of kinetic friction of 0.3, moving with an initial velocity of 20 m/s. What is the average thermal power generated as the object slows to a stop?

Four students run up the stairs as shown in the figure: Adam (mass of 80 kg) goes up 10 m in 10 s, Bob (80 kg) 10 m in 8 seconds, Claire (64 kg) 10 m in 8 s, and David (80 kg) 20 m in 25 s.
Who has the smallest power output?
A. Bob
B. Claire
C. David
D. Adam