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The constant force resisting the motion of a car of mass 1500kg is equal to one fifteenth of its weight. When travelling at 48km/h, the car is brought to rest in a distance of 50m by applying the brakes, find the additional retarding force due to the brakes (assumed constant) and heat developed in the brakes.

Given,
Mass of car (m) = 1500 kg
Frictional force (Fc) = 115m.g
                                      = 115150010=1000N
Initial velocity (u) = 48 km/hr = 4810006060 =13.33m/s
Distance covered (s) = 50 m
Final velocity (v) = 0
Additional force (Fa=?)
Heat developed in the engine = ?

To calculate, a=? We have,
v2=u2+2.a.s
02=(13.33)2+2a50
⇒ a =  (13.33)2250=1.78m/s

The retarding force due to friction is,
Fr=ma=1.781500=2666.67N
But frictional force (Fc=1000N)

So, Additional force (Fa) = FrFc=2666.671000=1666.67N

Now heat developed = ?
Heat developed = Work done
i.e. W=Fas=1666.6750=83333.33J

∴ Additional retarding force due to brake is 1666.67N
∴ Heat developed in the engine is 83333.33J

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