The human cannonball

Question

During a circus performance, a 71.5-kg human cannonball is shot out of an 17.5-m-long cannon. If the human cannonball spends 0.935 s in the cannon, determine the average net force exerted on him in the barrel of the cannon. (Assume the acceleration is constant.)

Answer 1

I like to start problems like this by writing out what we know:

1. m = 71.5 kg
2. d = 17.5 m
3. t = 0.935 s
4. v_i = 0 m/s (people always forget this one, but it's logical to assume that this human cannonball must start from rest at the bottom of the cannon.

Now, what are we solving for? F_net. Unfortunately, there's no single formula we can use to solve this straight-away. This will be a two-step problem, where first we use 1-d motion formulas to find "a", then use F = m*a to solve for F_net.

1. Step 1
2. Find an equation that includes a (since we need to find it), and some of the other "known" information.
3. d = v_i*t + 1/2 *a*t²
4. Plug in what you know and solve this for a.
5. Step 2
6. Go back to F_net = m*a, and plug in the acceleration you just found and given mass.
7. Solve for F_net and round to 3 significant figures (since the given info all has 3 sig. figs)