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Chapter 7: Q23Q (page 170)
How can a rocket change direction when it is far out in space and essentially in a vacuum?
When a rocket wants to change its direction, it ejects some gas opposite to the desired direction.
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An atomic nucleus of mass m traveling with speed v collides elastically with a target particle of mass 2m (initially at rest) and is scattered at 90°.
(a) At what angle does the target particle move after the collision?
(b) What are the final speeds of the two particles?
(c) What fraction of the initial kinetic energy is transferred to the target particle?
An object at rest is suddenly broken apart into two fragments by an explosion. One fragment acquires twice the kinetic energy of the other. What is the ratio of their masses?
A 0.450-kg hockey puck, moving east with a speed of 5.80 m/s, has a head-on collision with a 0.900-kg puck initially at rest. Assuming a perfectly elastic collision, what will be the speed and direction of each puck after the collision?
Air in a 120-km/h wind strikes head-on the face of a building 45 m wide by 75 m high and is brought to rest. If air has a mass of 1.3 kg per cubic meter, determine the average force of the wind on the building.
(a) Calculate the impulse experienced when a 55-kg person lands on firm ground after jumping from a height of 2.8 m.
(b) Estimate the average force exerted on the person’s feet by the ground if the landing is stiff-legged, and again
(c) with bent legs. With stiff legs, assume the body moves 1.0 cm during impact, and when the legs are bent, about 50 cm. [Hint: The average net force on him, which is related to impulse, is the vector sum of gravity and the force exerted by the ground. See Fig. 7–34.] We will see in Chapter 9 that the force in (b) exceeds the ultimate strength of bone (Table 9–2).
FIGURE 7-34 Problem 24.
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