Phy-102 Energy and Circular Exercises

Phy-102 Energy and Circular Exercises Question 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. b. Explain this using the work-energy theorem A. According to the impulse momentum the impulse must be dependent on the applied force. This is Impulse=applied force*time). The longer barrel allows the gases to expand more, which will push the bullet for longer. Which will have increased velocity and/or impulse. B. The same thing can really be explained with the work energy theorem. The WET states that work is equal to change in kinetic energy. The work (work-force distance), and the kinetic energy is the function of mass and velocity which is explained by (1/2 mv^2). The gases that are exerting a force on the bullet in a long rifle will be greater as the kinetic energy as the bullet is travelling a longer distance. So therefore the speed of the bullet will be greater, and be more powerful than the one with a shorter barrel. Question 2. Use physics terms to explain the benefits of crumple zones in modern cars. Crumple zones in cars are located in the front and back of the vehicles. The crumple zones are there to ultimately help reduce injuries in case of a serious crash. According to Newtons first law of motion, sometimes referred to as law of inertia, states that a body at rest will remain at rest, and a body in motion will remain in motion unless it is acted upon by and external source (). An example of this would be the commercials we see on TV when they are crash testing vehicles. The vehicles are shot out like a cannon straight into a wall, the car crashes, but the dummies inside stay in motion and move forward. When a car crashes, the goal is for the structure to crush in a relatively gradual, predictable way that absorbs much of the impact energy, keeping it away from the occupants in what is termed a controlled crush (). Question 3. When a gun is fired at the shooting range, the gun recoils (moves backward). Explain this using the law of conservation of momentum.