Question

The kinetic energy of a car is 8 × 106 J as it travels along a horizontal road. How much power is required to stop the car in 10 s?

Answer 1

The kinetic energy of a car is $8 \times 106 \, \text{J}$ as it travels along a horizontal road. How much power is required to stop the car in $10 \, \text{s}$?

Solution:

Power is the rate at which energy is transferred. You need to transfer 8 million joules of kinetic energy into 8 million joules of heat in the car's brakes in 10 seconds.

$$\text{Power} = \frac{\text{Change in Energy}}{\text{Time}}:$$ $$P = \frac{E}{t} = \frac{8 \times 10^6 \, \text{J}}{10 \, \text{s}} = 8 \times 10^5 \, \text{W}$$

Answer: required power to stop the car is $8 \times 10^{5} \, \text{W}$.