Exercise Set 2 Questions
Newton’s 2nd Law (Chapter 4)
1. A 4000-N bear grasping a vertical tree slides down at constant velocity. (i) Draw a
force diagram of the bear. (ii) What is the friction force that acts on the bear?
2. Jose accelerates away from a stop sign. His eight-year-old daughter sits in the
passenger seat. On whom does the back of the seat exert a greater force?
3. A racecar travels along a raceway at a constant velocity. What is the net force acting on
the car? Now the racecar goes around a curve at a constant speed. What is the net force
acting on the car now? Defend your answer.
4. Are the objects described here in static equilibrium, dynamic equilibrium, or not in
equilibrium at all?
a. A girder is lifted at constant speed by a crane.
b. A girder is lowered by a crane. It is slowing down.
c. You're straining to hold a 200 lb barbell over your head.
d. A jet plane has reached its cruising speed and altitude.
e. A rock is falling into the Grand Canyon.
f. A box in the back of a truck doesn't slide as the truck stops.
5. A person can dive into water from a height of 10 m without injury, but a person who
jumps off the roof of a 10-m-tall building and lands on a concrete street is likely to be
seriously injured. Why is there a difference?
6. A rock is thrown upward. What is the net force acting on the rock at the top of its
trajectory? What is the rock’s acceleration at the top?
7. If you drop a pair of tennis balls (one filled with air and the other filled with lead
pellets) simultaneously from the top of a building, will they strike the ground at the same
time? Which one will experience greater air resistance? Defend your answers.
Newton’s 3rd Law (Chapter 5)
1. For each of the following interactions, identify action and reaction forces. (i) A hammer
hits a nail. (ii) Earth gravity pulls down on a book. (iii) A helicopter blade pushes air
downward.
2. Why does a rope climber pull downward on the rope to move
upward?
3. Suppose two carts, one twice as massive as the other, fly apart
when the compressed spring that joins them is released. How fast
does the heavier cart roll compared with the lighter cart?
4. If you ask most people what force makes a car accelerate forward, they will say “the
force of the engine.” But what force is directly responsible for making the car accelerate?
5. Josh and Taylor, standing face-to-face on frictionless ice, push off each other, causing
each to slide backward. Josh is much bigger than Taylor. After the push, which of the
two is moving faster?
6. A small compact car is pushing a large van that has broken down, and they travel
along the road with equal velocities and accelerations. While the car is speeding up, is
the force it exerts on the van larger than, smaller than, or the same magnitude as the
force the van exerts on it? Which object, the car or the van, has the largest net force on
it, or are the net forces the same? Explain.
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