PHY-102: Energy and Circular Motion Exercises Questions and answers

PHY-102: Energy and Circular Motion Exercises Questions and answers Complete the following exercises. 1. A rifle with a longer barrel can fire bullets with a larger velocity than a rifle with a shorter barrel. a. Explain this using the impulse-momentum theorem. By the theory of momentum, change in momentum of an object equals the impulse applied to it meaning that the long barrel of the rifle covers a huge amount of motion of the bullet since the bullet receives more impulse from the expanding gases with an inch of length of the barrel compared to the short rifle. b. Explain this using the work-energy theorem By work-energy theorem, the work done by all forces acting a particle equals the change in the particle’s kinetic energy meaning that the discharge of the bullet caused is slower but has more power than the one with the short barrel. 2. Use physics terms to explain the benefits of crumple zones in modern cars. A crump zone is intended to slow down the crash, and also absorb energy to reduce the difference between the speed of the car occupants; traveling at speed due to momentum, and the car (abruptly stopped). 3. When a gun is fired at the shooting range, the gun recoils (moves backward). Explain this using the law of conservation of momentum. According to the law of conservation of momentum, the total momentum is unchanged. Hence, when the gun is fired, the bullets gain a high velocity forward that is positive velocity and that velocity multiplied by its mass equals the momentum gained. Therefore, the gun must gain a momentum backward to cancel out the forward momentum, so the gun recoils back with negative velocity.