Question
A 0.0250-kg bullet is accelerated from rest to a speed of 550 m/s in a 3.00-kg rifle. The pain of the rifle’s kick is much worse if you hold the gun loosely a few centimeters from your shoulder rather than holding it tightly against your shoulder. (a) Calculate the recoil velocity of the rifle if it is held loosely away from the shoulder. (b) How much kinetic energy does the rifle gain? (c) What is the recoil velocity if the rifle is held tightly against the shoulder, making the effective mass 28.0 kg? (d) How much kinetic energy is transferred to the rifle- shoulder combination? The pain is related to the amount of kinetic energy, which is significantly less in this latter situation. (e) Calculate the momentum of a 110-kg football player running at 8.00 m/s. Compare the player’s momentum with the momentum of a hard-thrown 0.410-kg football that has a speed of 25.0 m/s. Discuss its relationship to this problem.
1. $4.58 \textrm{ m/s}$
2. $31.5 \textrm{ J}$
3. $-0.491 \textrm{ m/s}$
4. $3.38 \textrm{ J}$
5. $p_p = 880 \textrm{ kg}\cdot\textrm{m/s}$, $p_b = 10.3 \textrm{ kg}\cdot\textrm{m/s}$
Solution Video

# OpenStax College Physics Solution, Chapter 8, Problem 38 (Problems & Exercises) (4:50)   