Question

The power of an engine which accelerates a car of mass 800 kg to a speed of 72 km/h from rest in 32 sec. is​

Answer 1

72 kph = 20 m/s

The formula for power is P = Fv where P = power, F = force and v is the speed.

Revising the formula to suit the given data

P = Fv but F = ma so

P = (ma)v but a = Δv / Δt so

P = m (Δv / Δt) v is the formula suiting the data given

P = 800 kg (72 kph – 0) / 32 s * 72 kph

P = 800 kg * (20 m/s / 32 s) * 20 m/s

P = 800 kg * 0.625 m/s^2 * 20 m/s

P = 500 N * 20 m/s

P = 10,000 Nm/s

P = 10,000 J/s

P = 10,000 Watts

The power of the engine is 10,000 Watts.

Answer 2

Question :-

An engine accelerate a car of mass 800kg to a speod of 72km/h. If the frictional force is 10N per tonne, the power developed by the engine is

Question from :-

Class 11  Chapter Work, Energy, Power And Collision

Solution :-

Speed of car ,  $v=72km/h=72 X5/18=20ms^{-1}$

$KE=1/2mv^{2} =1/2X800X400=400X400J$

$P=KE/Time=400X400/32=5000W=5kW$

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