Quiz 7 (Week 8) PHYS 104 (out of 10 marks) 1. Is it possible for a system to have negative elastic potential energy? a) Yes, since the choice of the zero potential energy level is arbitrary b) No, because the kinetic energy of the system must equal its potential energy and kinetic energy cannot be negative 0) No, because this would have no physical meaning (1) Yes, but only if the spring extends downwards. 2. Which forms of energy have a clear, well-dened state at which their values are zero? 3) Kinetic Energy and Spring Potential Energy b) Kinetic Energy and Gravitational Potential Energy 0) Gravitational Potential Energy and Spring Potential Energy (1) Kinetic Energy, Gravitational Potential Energy and Spring Potential Energy. 3. A ball is thrown straight up. At what point does the ball have the most mechanical energy? Ignore air resistance. a) At the highest point of its path b) When it is rst thrown 0) Just before it hits the ground (1) When the ball is halfway to the highest point of its path 6) Everywhere; the energy of the ball is the same at all of these points. 4. When friction is present, can it ever result in an increase in an object's kinetic energy? a) No, since friction is a non-conservative force b) No, since friction always acts to slow things down c) Yes, since friction causes things to warm up and heat is a measure of macroscopic kinetic energy (1) Yes, since friction acts to reduce relative motion and can increase the kinetic energy of a connected object while reducing the kinetic energy of the object it is connected to. 5. A 1600 kg elevator is raised at a constant speed through a vertical height of 20.0 m in 8.00 3. What is the power of the winch that raised the elevator upwards? a) 39 200 W b) 4 000 1/8 c) 313 600 J d) 15 680 N 6. (5 marks) You are playing paintball with friends and you are defending a fort and are perched at an elevation of 35.6 m above the ground. You spot a player on the opposite team on the ground and fire a paintball at them so that it leaves your paintball gun at 90 m/s at 23.40 above the horizontal. With what speed does the paintball strike the player