Question

On a level road, a scooterist applies brakes to slow down from a speed of

10 m/s to 5 m/s. if the mass of the scooter and the scooterist be 150 kg,

calculate the work done by the brakes.(Neglect air resistance and friction)​

Answer 1

Given:

On a level road, a scooterist applies brakes to slow down from a speed of 10 m/s to 5 m/s. The mass of the scooter and the scooterist be 150 kg.

To find:

Work done by the brakes ?

Calculation:

According to WORK-ENERGY THEOREM, the work done by the brakes can be calculated as the change in kinetic energy of the scooter.

$\sf \therefore \: work = \Delta KE$

$\sf \implies \: work = \dfrac{1}{2} m {v}^{2} - \dfrac{1}{2} m {u}^{2}$

$\sf \implies \: work = \dfrac{1}{2} m( {v}^{2} - {u}^{2} )$

$\sf \implies \: work = \dfrac{1}{2} \times 150 \times \{{(5)}^{2} - {(10)}^{2} \}$

$\sf \implies \: work = 75 \times \{25 - 100 \}$

$\sf \implies \: work = 75 \times \{ - 75 \}$

$\sf \implies \: work = - 5625 \: joule$

So, work done by brakes is -5625 joules