1 Which has greater momentum: a heavy truck at rest or a moving skateboard?
2. Why is a force that is applied for a short time more effective in karate?
3. Suppose a ball of putty moving horizontally with 1 kg*m/s of momentum collides with and sticks to an identical ball of putty moving vertically with 1 kg*m/s of momentum. What is the magnitude of their combined momentum?
4. In the preceding question, what is the total momentum of the balls of putty before and after the collision?
5. Betty (mass 40 kg), standing on slippery ice, catches her leaping dog (mass 15 kg), moving horizontally at 3.0 m/s. Show that the speed of Betty and her dog after the catch is about 0.8 m/s.
6. A railroad diesel engine weighs four time as much as a freight car. If the diesel engine coasts at 5 km/hr into a freight car initially at rest, show that the speed of the coupled engine and car is 4 km/h.
(Note that you don't have to know m to solve the problem.)
7. A 5-kg fish swimming a 1m/s swallows an absentminded 1-kg fish swimming toward it at a speed that brings both fish to a halt immediately after lunch. Show that the speed of the approaching smaller fish before lunch must have been 5 m/s.
8. Comic-strip Superhero meets an asteroid in outer space and hurls it at 800 m/s, as fast as a bullet. The asteroid is a thousand times more massive that Superhero. In the strip, Superhero is seen at rest after the throw. Taking physics into account, what would be the speed of his recoil?
9. An ice sail craft is stalled on a frozen lake on a windless day. The skipper sets up a fan as shown. If all the wind bounces backward from the sail, will the craft be set in motion? If so, in which direction?
10. Discuss whether or not your answer to the preceding exercise would be different if the air is brought to a halt by the sail without bouncing.
11. Cite an example in which a force is exerted on an object without doing work on the object.
12. A car is raised a certain distance in a service-station lift and therefore has potential energy relative to the floor. If it were raised twice as high, how much more potential energy would it have?
13. When the speed of a moving car is doubled, how much more kinetic energy does it have?
14. What is the source of energy in sunshine?
15. What is the ultimate source of energy for fossil fuels, dams, and windmills?
16. In the hydraulic machine shown, you observe that when the small piston is pushed down 10 cm, the large piston is raised 1 cm. If the small piston is pushed down with a force of 100N, what is the most weight that the large piston can support?
17. The roller coaster ride starts from rest a point A. Ran these quantities from greatest to least at each point:
a. Speed
b. KE
c. PE
18. Two people who weigh the same climb a flight of stairs. The first person climbs the stairs in 30 s, and the second person climbs them n 40 s. Which person does more work? Which uses more power?
19. A moving hammer hits a nail and drives it into a wall. If the hammer hits the nail with twice the speed, how much deeper will the nail be driven? If the hammer hits with three times the speed?
20. When the velocity of an object is doubled, by what factor is its momentum changed? By what factor is its kinetic energy changed?
21. You're on a rooftop and you throw one ball downward to the ground below and another upward. The second ball, after rising, falls and also strikes the ground below. If air resistance can be ignored, and if your downward and upward initial speeds are the same, how will the speeds of the balls compare upon striking the ground? (Use the idea of energy conservation to arrive at your answer.)
22. How does the tapered rim of a wheel on a railroad train allow one part of the rim to have a greater tangential speed than another when it is rolling on a track?
23. Inertia depends on mass; rotational inertial depends on mass and something else. What?
24. Calculate the torque produced by a 50-N perpendicular force at the end of a 0.2 m-long wrench.
25. Calculate the tension in qa horizontal string that whirls a 2-kg toy in a circle of radius 2.5 m when it moves at 3 m/s on an icy surface.
26. A small space telescope at the end of a tether line of length L move at linear speed v about a central space station.
a. What will be the linear speed of the telescope if the length of the line is reduce to 0.33L?
b. If the initial linear speed of the telescope is 12.0 m/s, what is its speed when pulled in to one-third its initial distance from the space station?
27. When you pedal a bicycle, maximum torque is produced when the pedal sprocket arms in the horizontal position, and no torque is produced when they are in the vertical position. Explain.
28. The centers of gravity of the three trucks parked on a hill are shown by the X's. Which truck(s) will tip over?
29. Why does a typical small helicopter with a single main rotor have a second small rotor on its tail? Describe the consequence if the small rotor fails in flight.
30. A large wheel is coupled to a wheel with half the diameter, as shown in the sketch. How does the rotational speed of the smaller wheel compare with that of the larger wheel? Discuss the comparisons of the tangential speeds at the rims (assuming the belt doesn't slip).
31. When a car drives off a cliff it rotates forward as it falls. For a higher speed off the cliff discuss whether the car will rotate more or less. (Consider the time that the unbalanced torque acts.)
What did Newton discover about gravity?
What is the Newtonian synthesis?
In what sense does the Moon "fall"?
State Newton's law of universal gravitation in words. Then do the same with one equation.
32. Do tides depend more on the strength of gravitational pull or on the difference in strengths? Explain.
33. Why are all tides greatest at the time of a full moon or new moon.
34. Many people mistakenly believe that astronauts who orbit earth are "above gravity." Calculate g for space shuttle territory, 200 km above Earth's surface. Earth's mass is 6.0 x 1024 kg, and its radius is 6.38 x 106 m (6380 km). Your answer is what percent of 9.9 m/s2?
35. Gravitational force acts on all bodies in proportion to their masses. Why then, doesn't a heavy body fall faster than a light body?
36. Larry weighs 300 N at the surface of Earth. What is the weight of Earth in the gravitational field of Larry?
37. Why aren't high ocean tides exactly 12 hours apart?
38. Why does the vertical component of velocity for a projectile change with time, whereas the horizontal component of velocity doesn't?
39. Why doesn't the force of gravity change the speed of a satellite in circular orbit?
40. For orbits of greater altitude, is the period longer of shorter?
41. What did Kepler discover about the periods of planets and their distances from the Sun?
42. Escape speed from Earth is 11.2 km/s. Is it possible to escape from Earth at half this speed? At one-quarter this speed? If so how?
43. A ball is thrown horizontally from a cliff at a speed of 10 m/s. You predict that its speed 1 s later will be slightly greater than 14 m/s. Your friend says it will be 10 m/s. Show who is correct.
44. You're in an airplane that flies horizontally with speed 1000 km/h (280 m/s) when an engine falls off. Ignore air resistance an assume it takes 30 s for the engine to hit the ground.
a. Show that the airplane is 4.5 km high.
b. Show that the horizontal distance the aircraft engine moves during its fall is 8400 m.
c. If the airplane somehow continues to fly as if nothing had happened, where is the engine relative to the airplane at the moment the engine hits the ground?