science enerygy questions..please!!?

Question

1. Explain why long range cannons have long barrels.


2. A flight attendant and a passenger toss a ball back and forth in a moving airplane. Does the kinetic 9. At what point in its motion is the kinetic energy of a pendulum bob at a maximum? ______ At what point is its potential energy at a maximum? ________ When its kinetic energy is half its maximum value, how much potential energy does it have?

3. A physics instructor demonstrates energy conservation by releasing a heavy pendulum bob and allowing it to swing to and fro. What would happen if in her exuberance, she gave the bob a slight shove as it left her nose? Explain

Answer 1

1. To build up kinetic energy.
The longer the propellant applies force to the projectile the more kinetic energy the projectile will attain. As soon as the projectile left the barrel it only experiences a force of gravity :-)

2.The kinetic energy of a pendulum bob at a maximum at the lowest point of the swing.
I this case total kinetic energy equal to the sum of kinetic energy Ke and potential energy Pe
P (max)= Pe + Ke
So if Ke=1/2 P (max)
The Pe is the other half

3. While amplitude can change the period is
T=2pi sqrt (L/g) and is fixed by length L and acceleration due to gravity g.