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Question:

An automobile moves on a road with a speed of 54 km/h. The radius of its wheel is 0.45 m and the moment of inertia of the wheel about its axis of rotation is 3 kgm². If the vehicle is brought to rest in 15 s, the magnitude of average torque transmitted by its brakes to the wheels is:

10.86kgm²s

2.86kgm²s

6.66kgm²s

8.58kgm²s

Solution:

Torque = moment of inertia × angular acceleration
or τ = Iα
or τ = Ia/r = Iv/tr = 3(54 × 1000/3600)/15 × 0.45 = 6.66 kgm²s