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# want a quick help

If a car engine makes a car of mass 1500 kg move with a constant velocity of 5m/s and the force of friction is 1000 N then what is the power of the engine?

a. 5kW

b.7.5kW

c.15kW

d.75kW

if you get answer other than 5kW then please mention the solution also. Require the solution in maximum 3 hrs. if you can. thank you.

Note by Ansh Bhatt
2 years, 11 months ago

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Sort by:

• Instantaneous power = $$F*v = 1000*5 = 5kW$$(at start)

• Average power = $$\dfrac{Work \quad done}{time}$$

W = Force* displacement

Acceleration = F/m = 2/3 $$m/s^2$$

Now using third equation of motion (final velocity = 0)

$$v^2 = u^2 + 2as$$

$$s = \frac{u^2}{2a} = \frac{75}{4}$$ (body is decelerating)

By first equation of motion

$$t = u/a = \frac{15}{2} s$$

$$P_{avg} = \dfrac{1000*75/4}{15/2} = 2.5kW$$

- 2 years, 11 months ago

Thank you. @Krishna Sharma

- 2 years, 11 months ago