University:
Texas State University
Course:
PHYS 1310 | Elementary Physics I.
Academic year:

2020
Views:

372

Pages:

4
Author:

Marilyn James

Questions & Answers 1. Two gliders with the initial velocities and masses shown below hit each other in a perfectly elastic collision (elasticity 1.0). What will be the velocity of glider 2 after the collision? A. 0.0 m/s B. 2.0 m/s C. 4.0 m/s D. 6.0 m/s Correct Answer: D. 6.0 m/s Explanation: Because the gliders have the same mass and the collision is perfectly elastic, the gliders will exchange velocities. This means that the velocity of Glider 2 after the collision will be equal to the velocity of Glider 1 before the collision. You answered this question correctly! 2. Glider 1 starts with a mass of 2.4 kg and a velocity of 3.0 m/s. What is Glider 1's starting momentum? A. 2.4 kg•m/s B. 5.4 kg•m/s C. 7.2 kg•m/s D. 10.8 kg•m/s Correct Answer: C. 7.2 kg•m/s Explanation: Momentum is equal to mass times velocity, so . You answered this question incorrectly. Your answer was A. 3. Given the starting conditions shown below and a perfectly elastic collision, what will be the total momentum of both gliders after they collide? A. -7.0 kg•m/s B. -9.0 kg•m/s C. -13.0 kg•m/s D. -21.0 kg•m/s Correct Answer: B. -9.0 kg•m/s Explanation: By conservation of momentum, the total momentum after the collision is equal to the total momentum before the collision. The momentum of glider 1 before the collision was The momentum of glider 2 before the collision was Therefore the total momentum before and after the collision was You answered this question correctly! 4. Two balls collide head-on on a table. The rst ball has a mass of 0.50 kg and an initial velocity of 12.0 m/s. The second ball has a mass of 0.75 kg and an initial velocity of -16.0 m/s. After the collision, the rst ball travels at a velocity of -21.6 m/s. What is the velocity of the second ball after the collision? Assume a perfectly elastic collision and no friction between the balls and the table. A. 6.4 m/s B. 11.3 m/s C. 17.8 m/s D. 21.6 m/s Correct Answer: A. 6.4 m/s Explanation: For any elastic collision, the approach velocity is equal to the separation velocity. The approach velocity is equal to the difference of the two velocities, . Therefore, the approach velocity is The separation velocity is equal to the difference of the two velocities after the collision, . We know that the separation velocity is equal to the approach velocity, and the velocity of the rst ball is given. You answered this question correctly! 5. Two gliders collide on an air track. Glider 1 has a mass of 7.0 kg, and glider 2 has a mass of 4.0 kg. Before the collision, glider 1 had a velocity of 2.0 m/s, and glider 2 had a velocity of -5.0 m/s. If the collision is perfectly elastic, what is the total kinetic energy of both gliders after the collision? A. -36.0 J B. 36.0 J C. 64.0 J D. 128.0 J Correct Answer: C. 64.0 J Explanation: In any collision, the total amount of energy in the system is conserved. If the collision is perfectly elastic, no heat or sound is produced and the total kinetic energy is conserved. Therefore, the total kinetic energy after the collision is equal to the total kinetic energy before the collision. Kinetic energy is equal to , Therefore, the total kinetic energy before and after the collision is 64.0 J. You answered this question incorrectly. Your answer was A.