Physics Momentum
MOMENTUM QUESTIONS
1. Which has greater momentum: a train at rest or a moving skateboard? Since the train is not moving, it has zero momentum. The skateboard, as long as it has some speed, will have more momentum, since p = m*v. 2. What are the ways to increase impulse? Impulse depends on the magnitude of the applied external force and the time that the force acts on the system. By increasing either of those, impulse on a system will be increased, and the system’s momentum will change accordingly. 3. For the same force, why does a long rifle impart more speed to a bullet than a short pistol? The long barrel means that the force of the expanding gases from the gunpowder is able to push for more time on the bullet (since the push will continue as long as the bullet is in the barrel). Impulse = (Applied Force)*(time) 4. When you are in the way of a moving object and a collision is sure to occur, are you better off decreasing its momentum over a short time or over a long time? Explain. The amount of force you will feel is the same as the force you apply to the object. So if you decrease its momentum over a long time, less force is needed to act. So, you would be “better off” exerting a small force for a long time. 5. Why is it a good idea to have your hand extended forward when you are getting ready to catch a fast-moving baseball with your bare hand? Having your hand forward means that you can move your hand back with the ball, slowing it down over a greater distance – and also over a greater time. This reduces the force you need to apply to the ball, and consequently reduces the force you feel. 6. Why would it be a poor idea to have the back of your hand up against the outfield wall when you catch a long fly ball? The ball will be moving pretty quickly, so to stop it you will need to remove quite a bit of momentum. If your hand is against the wall, the ball will be stopped very quickly since there is not much room for your hand to move while stopping the ball. (In
1. Which has greater momentum: a train at rest or a moving skateboard? Since the train is not moving, it has zero momentum. The skateboard, as long as it has some speed, will have more momentum, since p = m*v. 2. What are the ways to increase impulse? Impulse depends on the magnitude of the applied external force and the time that the force acts on the system. By increasing either of those, impulse on a system will be increased, and the system’s momentum will change accordingly. 3. For the same force, why does a long rifle impart more speed to a bullet than a short pistol? The long barrel means that the force of the expanding gases from the gunpowder is able to push for more time on the bullet (since the push will continue as long as the bullet is in the barrel). Impulse = (Applied Force)*(time) 4. When you are in the way of a moving object and a collision is sure to occur, are you better off decreasing its momentum over a short time or over a long time? Explain. The amount of force you will feel is the same as the force you apply to the object. So if you decrease its momentum over a long time, less force is needed to act. So, you would be “better off” exerting a small force for a long time. 5. Why is it a good idea to have your hand extended forward when you are getting ready to catch a fast-moving baseball with your bare hand? Having your hand forward means that you can move your hand back with the ball, slowing it down over a greater distance – and also over a greater time. This reduces the force you need to apply to the ball, and consequently reduces the force you feel. 6. Why would it be a poor idea to have the back of your hand up against the outfield wall when you catch a long fly ball? The ball will be moving pretty quickly, so to stop it you will need to remove quite a bit of momentum. If your hand is against the wall, the ball will be stopped very quickly since there is not much room for your hand to move while stopping the ball. (In