The power of engine of a car of mass 1200 kg is 25kW. The minimum time required to reach a velocity of 90km/he by the car after starting from rest is-???

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Solution

Given, m = mass of the car = 1200 kg

P = power of the engine of the car = 25 kW = 25000 Watt

v₀ = initial velocity of the car = 0 m/s

v = final velocity of the car = 90 km/h = 901000/(6060) = 900/36 = 25 m/s

Using work-change in kinetic energy theorem

W = work done = change in kinetic energy = 1/2 * m (v² - v₀²)

We know, workdone = Power x time = P t

Hence, P t = 1/2* m (v² - v₀²)

inserting the values

(25000) t = 1/2 * (1200) (25² - 0²)

25000 t = 600 x 625

t = 600 x 625/ 25000 = 15 seconds

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