Answer to Question #96774 in Classical Mechanics for Jeeva Gill

Question

A man sits in a cannon barrel and lights the fuse. A force of 6000N propels him out of the barrel (which is 2.5m long) in 0.35s. The man has a mass of 85kg. What is the man’s velocity as he leaves the cannon?

Answer 1

Let the man’s velocity as he leaves the cannon be $v$, time of the force action be $t$ , the force acting on the man be $F$ , mass of the man be $m$ .

Impulse of the man when he leaves the barrel is

$J=m\cdot v=F\cdot t,$ therefore

$v=\frac{F\cdot t}{m}=6000\cdot0.35/85\approx 24.7 m/s$

Answer: $24.7 m/s.$

Conditions of the problem contradict each other:

Since the force $F$ is constant, the acceleration of the man should be constant and time to leave the barrel should be $t=\frac{2l}{v}=\frac{2\cdot2.5}{24.7}\approx0.2s.$