1. For unknown reasons, you are standing on a bathroom scale in an elevator. As the elevator accelerates downwards, does the scale read higher or lower than your normal weight? Explain your answer in terms of forces and Newton's laws.
2. When a kangaroo leaps forward, what is the force that accelerates the kangaroo, and what is the direction of that force?
3. A baseball batter hits a line drive into center field.
(a) Which is larger, the force on the bat or the force on the ball?
(b) Which has a greater acceleration, the bat or the ball? Explain your answer for both parts.
4. A large crate full of rubber chickens is being lifted off the top shelf in a warehouse by a forklift.
(a) Is the force provided by the forklift greater when the crate is held at a constant height, or when the crate is moving downward at constant velocity?
(b) As the crate is moving down, is the force provided by the forklift greater when the crate is speeding up or when the crate is slowing down? Explain both answers in terms of Newton's Laws.
5. The world-record flight for a "human cannonball," set by David Smith Jr. on March 10, 2011, covered a distance of 59 m. During the launch, Mr. Smith reached a speed of 120 km/h in a cannon 8 m in length. Assuming David had a mass of 80 kg, what was the average force on him during the launch?
6. The position r of a particle of mass m moving at speed v in a circular path of radius R is given by
r = R cos(vt/R)x^+ R sin(vt/R)y^.
Derive the equation for the centripetal force F acting on this particle.
7. Bubba's fully loaded garbage truck (m = 25, 000 kg) is moving down the road at 25 m/s when a personal-injury lawyer steps into the street 200 meters ahead of him. He ponders whether to hit the brakes or the gas for 2.5 seconds, then hits the brakes, which apply a force of 62,500 N (backwards) on the garbage truck.
(a) Does Bubba run over the lawyer?
(b) If not, how far away is the lawyer when Bubba stops? If Bubba does hit the lawyer, how fast is he going?
8. An 80-kg cyclist is rolling down an 8% grade at 34 mph. At this speed, the apparent headwind produces a force of 120 N. To maintain his speed, how much extra force should the cyclist apply to the road, and should he apply that force by pedaling harder, or by grabbing the brakes?
9. Tarzan is swinging to the rescue once again. He swoops down on a vine and at the very bottom of the swing he picks a baby koala from the ground just before it is eaten by a grizzly bear. Ignoring the "only-in-a-Disney-movie" probabilities involved, draw free-body diagrams for Tarzan and for the baby koala at the moment of the rescue. Indicate which of the forces are third-law pairs.
