A car moves on a road with a speed of `54 km h^(-1)`. The radius of its wheels is `0.35 m`. What is the average negative torque transmitted by its brakes to the wheels if the car is brought to rest in `15 s`? Moment of inertia of the wheels about the axis of rotation is `3 kg m^(2)`.

Explanation

Given, u=54 km/h =15m/s
R=0.35m,t =15s
`I=3kgm^(2)`
`omega_(i)=(u)/(R)=(15)/(0.35)` rad/s
`omega_(f)=0`
Average angular acceleration is:
`alpha=(omega_(f)-omega_(i))/(t)=(0-(15)/(0.35))/(15)=-(1)/(0.35)rad//s^(2)`
Average negative torque transmitted by the brakes is
`tau=I.alpha=3xx(-(1)/(0.35))=-8.57kgm^(2)s^(-2)`