Imagine a system in which two clay balls of mass m1 and m, have been thrown toward each other. As each ball reaches the highest point In its trajectory, the balls collide with each other and stick together. We want to find the velocity of the stuck-together balls. \"I m; .._---o o.___ 'a r I- N z ' Iv, v, \"a 1. Choose the statement that is true: A. Conservation of Linear Momentum cannot be used because gravity is an external force that acts before, during and after the collision. B. Conservation of Linear Momentum will apply from the time when the balls are thrown until the time they hit the ground. Conservation of Linear Momentum will apply for a very short time before and after the collision. D. Since gravity is the only force on the system, we should use Conservation of Mechanical Energy, not Conservation of Linear Momentum. E. Conservation of Linear Momentum does not apply because the balls do not move in a straight line. 5" Two carts with frictionless wheels are on a level surface. One cart with m, = 1 kg is at rest and the other with or; = 2 kg is moving toward it at v, = 20 chs. They collide and stick together. ml "'2 "1:0 vz=20cmls I\"? _E_"E_E_ Before collision After collision Important note: The text of Q2 in the lecture video has the masses flipped. It should say m1 = 2 kg and 1112 = 1 kg. 2. What is the speed of the carts after the collision? A. %(2 kg)(i2l}2 + \"(1 kg)(20 cm/s)2 = 1/z(3 kg)(v}2 so speed = 12 cm/s B. (2 kg)(0} + (1 kg)(2[l cm/s) = (3 kg}{v) so speed = 5.7 cm/s C. 145(2 kg)(i2l}2 + (2 kg)(0} + 1AU kg)(20 cm/s)2 + (1 kg)(20 cm/s) = 1/z(3 kg)(v)2 + (3 kg)(v) so speed = 11 cm/s D None of the above answers is correct. Two carts with frictionless wheels are moving on a level surface. Cart 1, the red cart, has a mass m, = 1 kg and a velocity of 10 cm/s. Carl: 2, the green cart, has a mass m2 = 2 kg and is moving at v, - -15 cm/s. After the collision they move apart. m1 m2 '1 = 10 CMIS v2 = -15 cm/s "mm "'1 \"'2 y: a". b' h ' . Before collision After collision 3. What type of collision is it? A. This is an elastic collision. B This is an inelastic collision. C. This is a perfectly (or totally) inelastic collision. D. This is an explosive (or superelastic) collision. E. Not enough information is given to answer it. Additional Questions to test your understanding [Conservation of momentum) 4. In a perfectly Inelastic collision (choose all that apply): A. Linear momentum is conserved. B. Kinetic energy is conserved. C. The objects stick together after the collision. D. The objects don't stick together after the collision. 5. In an inelastic collision (choose all that apply): A. Linear momentum is conserved. B Kinetic energy is conserved. C. The objects stick together after the collision. D. The objects don't stick together after the collision. 6. In an elastic collision (choose all that apply): A. Linear momentum is conserved. B. Kinetic energy is conserved. C. The objects stick together after the collision. D. The objects don't stick together after the collision. 7. One railroad car is travelling to the right at speed v. It collides into an identical railroad car which is at rest, and after the collision, they lock together. What is their common speed after the collision? A. v C. ole NH: le 8. 9. 10. 11. In the previous question, was kinetic energy conserved during the collision? Hint: You can easily gure out the initial and final kinetic energies. Do NOT use your intuition! A. Yes B. No C. Cannot determine without the numerical values of m and v. A person of mass 175 lbs. runs and jumps into a stationary cart of mass 300 lbs. The initial speed ofthe person is 8 m/s. What is the nal speed ofthe cart after the person jumps in? Express your answer in m/s and input the number only. What is the change in kinetic energy from before to after the collision of the system (person + cart)? Express your answer in] and input the number only. If it's negative, input the minus sign. Hint: Don't forget to convert! A 2.0 kg block is moving towards the right on a frictionless table at an initial speed vi=6 m/s . It collides elastically with another object of the same mass. After the collision what are the speeds of the two blocks? Hint: This is an elastic collision, meaning that two quantities are conserved. Which of the options below conserves both? A. 3 m/s and 3 m/s 3 m/s and 3 m/s - Vi - 0 m/s and 3 m/s 0 m/s and 6 m/s 2 m/s and 4 m/s woman Hint1: This is an elastic collision, meaning that m momentum and kinetic energy must be conserved. For each answer choice, figure out if this is the case. We know the initial momentum is (2.0 kg) (6 m/s) = 12 kg m/s to the right and the initial kinetic energy is 0.5 (2.0 kg) (6.0 m/s)2 = 36 J. Hintz: For example: Choice A: final momentum = 2 kg (3 m/s) + 2 kg (3 m/s) = 6 kg m/s -> same as initial -> it's conserved final kinetic energy = 0.5 (2 kg) (3 m/s)2 + 0.5 (2 kg) (3 m/s)2 = 18 J-> not the same as initial -> not conserved. So answer choice A cannot be correct because kinetic energy is not conserved