Question

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

Answer 1

$power = \frac{work \: done}{total \: time \: taken}$
$and \\ work \: done = change \: in \: kinetic \: energy$
$work \: done = \frac{1}{2} m {v}^{2} - \frac{1}{2} m {u}^{2} \\ since \: object \: starts \: from \: rest \: then \: \: \: u = 0 \\ work \: done = \frac{1}{2} m {v}^{2}$

$power = \frac{ \frac{1}{2} m {v}^{2} }{total \: time} \\ \\ 2\times {10}^{ 3} joules {sec}^{ - } = \frac{1200 \times {25}^{2} }{time} \\ time = \frac{30 \times {10}^{3} }{2 \times {10}^{3} } \\ time = 15sec$

Time required =15 seconds.

since, watt =1 joules/sec then to make solution in proper units we convert velocity in m/sec.

Answer 2

Answer:

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