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)

Given,

Mass of scooter + scooterist, (m) = 150 kg 
Initial velocity, (u) = 10 m/s
Final velocity, (v) = 5 m/s
Retardation = a
Distance covered = s

Using the third equation of motion,
${v}^{2}-{u}^{2}=2as$
${5}^{2}-{10}^{2}=2as$
$25-100=2as$
$-75=2as$
$as=\frac{-75}{2}$     --------- (i)
Now,
Work done, $W=F\times s$
$W=m\times a\times s$    [putting the value of $F=m\times a$]
$W=150\times (\frac{-75}{2})$  [putting the value of $as$ from (i)]
$W=-5625J$
The negative sign implies that force applied by the brakes is acting opposite to the direction of motion.

Updated on: 10-Oct-2022

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