In a very popular lecture demonstration, a projectile is fired at a falling target as in Figure P3.59. The projectile leaves the gun at the same instant that the target is dropped from rest. Assuming that the gun is initially aimed at the target, show that the projectile will hit the target. (One restriction of this experiment is that the projectile must reach the target before the target strikes the floor.)
In a very popular lecture demonstration, a projectile is fired at a falling target as in Figure P3.59. The projectile leaves the gun at the same instant that the target is dropped from rest. Assuming that the gun is initially aimed at the target, show that the projectile will hit the target. (One restriction of this experiment is that the projectile must reach the target before the target strikes the floor.)
If you know the drop distance of the target you can calculate thefinal velocity of the target before it reaches the ground, or howfast it is moving when the projectile strikes.
Use kinematics:
Start by finding the final velocity using
VF2=VI2+2a(D)
Here your initial velocity is 0 because it was at rest andacceleration is due to gravity -9.80 m/s2
Once you solve for your final Velocity you can calculate timeusing
VF=VI + a(T)
Again acceleration is due to gravity -9.80m/s2
Now that you know the time it takes your target to reach the impactpoint you can use time for solving the rest of the problem.
You will need to know the velocity of the projectile to finish offthe problem because that will determine the distance you will needto fire the projectile from. Was that detail given to you in theproblem or are you simply proving the theory?
If you are only proving theory then just remember that in projectile motion the only force acting on the projectile is gravity, and that if two similarly shaped, and similarly massed objects are dropped from the same height they will fall at about the same rate (unless in a vacuum).
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