Page 113 - Schaum's Outline of Theory and Problems of Applied Physics

98 MOMENTUM [CHAP. 8

8.9. The trucks in Question 8.8 are headed in opposite directions when they collide. The trucks again stick together, and
the wreckage now has an initial velocity of
(a) 9.1 km/h (c) 48 km/h
(b) 42 km/h (d) 53 km/h

8.10. The trucks in Question 8.8 lost a total KE that is
(a)0
(b) less than the KE lost by the trucks in Question 8.9
(c) the same as the KE lost by the trucks in Question 8.9
(d) more than the KE lost by the trucks in Question 8.9
8.11. An 800-kg car headed south at 40 km/h strikes a 1200-kg car headed west at 25 km/h. The cars stick together and the
initial velocity of the wreckage is
(a) 22 km/h (c) 33 km/h
(b) 31 km/h (d) 47 km/h

8.12. The wreckage of Question 8.11 moves off at
◦
◦
(a) 20 WofS (c) 47 WofS
◦
◦
(b) 43 WofS (d) 70 WofS
8.13. A ball is dropped from a height of 300 cm. If the coefficient of restitution is 0.600, the ball rebounds to a height of
(a) 104 cm (c) 134 cm
(b) 108 cm (d) 180 cm

Supplementary Problems

8.1. Find the momentum of a 100-kg ostrich running at 15 m/s.

8.2. Find the momentum of a 3200-lb car moving at 60 mi/h (88 ft/s).

8.3. An object at rest explodes and breaks up into two parts that fly off. Must they move in opposite directions?
8.4. A moving object strikes a stationary one. After the collision, must they move in the same direction?

8.5. A 2500-kg truck crashes into a wall at 40 km/h and comes to a stop in 0.5 s. What is the average force on the truck?

8.6. A 5-kg rifle and a 7-kg rifle fire identical bullets with the same muzzle velocities. Compare the recoil momenta and
recoil velocities of the two rifles.

8.7. An empty dump truck is coasting with its engine off along a level road when rain starts to fall.
(a) Neglecting friction, what (if anything) happens to the velocity of the truck?
(b) The rain stops and the collected water leaks out. What (if anything) happens to the velocity of the truck now?

8.8. A 60-kg woman dives horizontally from a 250-kg boat with a velocity of 2 m/s. What is the recoil velocity of the boat?
8.9. Four 50-kg girls simultaneously dive horizontally at 2.5 m/s from the same side of a boat, whose recoil velocity is
0.1 m/s. What is the mass of the boat?
8.10. A spacecraft’s motors provide a total thrust of 1.5 MN. If the exhaust speed is 2.5 km/s, at what rate is fuel being used?