Question

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

Answer 1

m = mass of the car = 1200 kg

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

t = time taken by the car to reach a velocity of 90 km/h starting from rest = ?

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

v = final velocity of the car = 90 km/h = 90(5/18) = 25 m/s

Using work-change in kinetic energy theorem

W = work done = change in kinetic energy = (0.5) m (v² - v₀²)

P t =  (0.5) m (v² - v₀²)

inserting the values

(25000) t = (0.5) (1200) (25² - 0²)

t = 15 sec

Answer 2

Hi there!


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Given :



Initial velocity (u) = 0



Final velocity (v) = 90 km/h = 25m/s.



Mass of car = 1200 kg.



Power of engine = 25 kW = 25000 W



We know that..



Power = work done / time



Work done = 1 / 2 mv²



=> 1/2 × 1200 × 25 × 25



=> 600 × 625



=> 375000 Joule.



Now,



Time = work done / power



Time = 375000 / 25000



Time = 15 secs.



Hence, the required time is 15 secs.




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Thanks for the question!



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