Power

Question 1

Define Power.

Answer 1

The rate of transfer of energy.

Question 2

Why is power measured in Watts?

Answer 2

Because power is equal to the change in energy over change in time (J/s). P (W) = ∆E (J) / ∆t (s)

Question 3

What is the equation for the power of an engine/ vehicle?

Answer 3

P (J/s) = F (N) x v (m/s)

Question 4

How is the motive power of an object calculated?

Answer 4

Motive Power (W) = Energy wasted per second (W)+ gain of kinetic energy per second (W)

Question 5

The engine of a train travelling at a constant velocity is providing a force of 10kN, and transfers 1.08 MJ every second. There is a drag force of 1,000N acting against the train. Calculate the distance the train travels over 3 seconds.

Answer 5

Power output of engine = ∆E / ∆t = 1,080,000/3 = 360,000W. Constant velocity, v, = P/F, = 360,000/(10,000-1,000), = 40 m/s. d=st, d= 40 x 3 = 120m.