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Home  >>  JEEMAIN and AIPMT  >>  Physics  >>  Class11  >>  Work, Power and Energy
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From an automatic gun a man fires 360 bullets per minute with speed of 360 km/hr. If each weighs 20g the power of gun

\[(a)\;600\;W \quad (b)\;300\;W \quad (c)\;150\;W \quad (d)\;75\;W\]

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Answer: 600 W
Power of a body is defined as the rate at which the body can do the work.
Power $ = \large\frac{W}{t}$, where work done $W = F \times d = m \times a \times d$
360 bullets are fired in one minute $\rightarrow$ time taken for firing 1 bullet $ t = \large\frac{60}{360} $ $ = \large\frac{1}{6}\;$$s$
Now, $v = u + a t$, but $u = 0$ as the bullet starts from rest and $v = 360 km/hr = 100 m/s$
$\Rightarrow 100 = 0 + a \large\frac{1}{6}$$ \rightarrow a = 600 m/s^2$
we can use the kinematic equation $s = ut + \large\frac{1}{2}$$ at^2$ to calculate the distance.
$\Rightarrow s = 0 + \large\frac{1}{2}$$ 600\;m/s^2 \times \large (\frac{1}{6})^2$$ = \large\frac{25}{3}$$m$
$\Rightarrow P = \large\frac{W}{t}$$ = \large\frac{ 20g \times 600 m/s^2 \times \Large\frac{25}{3}}{\Large \frac{1}{6}}$$ = 600W
answered Jul 18, 2013 by meena.p
edited Aug 27, 2014 by balaji.thirumalai

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