Page 1599 - College Physics For AP Courses

Answer Key 1587
Figure 4.4. Car X is shown on the left, and Car Y is shown on the right. i.
Car X takes longer to accelerate and does not spend any time traveling at top speed. Car Y accelerates over a shorter time and spends time going at top speed. So Car Y must cover the straightaways in a shorter time. Curves take the same time, so Car Y must overall take a shorter time.
ii.
The only difference in the calculations for the time of one segment of linear acceleration is the difference in distances.
That shows that Car X takes longer to accelerate. The equation corresponds to Car Y traveling for a time at
top speed.
Substituting into the displacement equation in part (b) ii gives . This shows that a car takes less

time to reach its maximum speed when it accelerates over a shorter distance. Therefore, Car Y reaches its maximum
speed more quickly, and spends more time at its maximum speed than Car X does, as argued in part (b) i.
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A body cannot exert a force on itself. The hawk may accelerate as a result of several forces. The hawk may accelerate toward Earth as a result of the force due to gravity. The hawk may accelerate as a result of the additional force exerted on it by wind. The hawk may accelerate as a result of orienting its body to create less air resistance, thus increasing the net force forward.
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(a) A soccer player, gravity, air, and friction commonly exert forces on a soccer ball being kicked.
(b) Gravity and the surrounding water commonly exert forces on a dolphin jumping. (The dolphin moves its muscles to exert a force on the water. The water exerts an equal force on the dolphin, resulting in the dolphin’s motion.)
(c) Gravity and air exert forces on a parachutist drifting to Earth.
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(c)
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Figure 4.14.
The diagram consists of a black dot in the center and two small red arrows pointing up (Fb) and down (Fg) and two long red arrows pointing right (Fc = 9.0 N) and left (Fw=13.0 N).
In the diagram, Fg represents the force due to gravity on the balloon, and Fb represents the buoyant force. These two forces are equal in magnitude and opposite in direction. Fc represents the force of the current. Fw represents the force of the wind. The net force on the balloon will be N and the balloon will accelerate in the
direction the wind is blowing.
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