First slide

Power

Question

A 500kg car ,moving with a velocity of $36 k m h^{- 1}$ on a straight road undirectionally, doubles its velocity in 1min. The average power delivered by the engine for doubling the velocity is

Moderate

A

750 W
B

1050 W
C

1150 W
D

1250 W

Solution

$i n i t i a l v e l o c i t y u = 10 m s^{- 1}, f i n a l v e l o c i t y v = 20 m s^{- 1}$
Work done = Increase in kinetic energy
Work = $\frac{1}{2} m [v^{2} - u^{2}] =$ $\frac{1}{2}$ x500 $[20^{2} - 10^{2}]$ = $\frac{500 \times 30 \times 10}{2}$

Powere = $\frac{∆ K E}{T i m e}$
Power = $\frac{500 \times 30 \times 10}{2 \times 60}$ = 1250W

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