Question

A car moving at a constant speed of $54km/h$ comes to rest in $2.5seconds$. The car covers $5m$ after driver applies the brakes. The total force applied to stop the car is $1000N$. Calculate the power dissipated in stopping the car.

• A. $1kW$
• B. $2kW$
• C. $3kW$
• D. $5kW$

Answer 1

The correct option is B $2kW$

Given,
Total force applied to stop the car is $1000N$
Distance covered by the car before stopping (s) $=5m$
Time taken by the car to come to rest $=2.5seconds$

$\Rightarrow$ Work done to stop the car (W) = Force × Displacement
$\Rightarrow W=1000\times 5=5000N$


We know that power is defined as the work done per unit time,
$\Rightarrow Power=\frac{Workdone}{Time}$

$\Rightarrow Power=\frac{5000}{2.5}$

$\Rightarrow Power=2000W=2kW$

Therefore, option B is the correct answer.