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Chapter 3 Homework

1.Due to what property does a body display the tendency to stay in the state of rest or motion?

2.The recoil experienced when firing a gun is a consequence of which law?

3.You are standing between 2 skaters. Skater 1 has a mass of 30 kg and skater 2 has a mass of 90 kg. If you push them both with an equal force who will have the greatest acceleration and by how much?

4. What keeps the Moon in its orbit around the Earth?

5.If you double the distance between two bodies, what happens to the force of gravity between them? What happens if you triple the distance? Make the distance 20 times greater?

6.Why does an astronaut feel weightlessness in space? What happens to the astronaut's mass in space?

7.Where at sea level on Earth will you weigh the least? Why?

8.What do we call the speed an object needs to move away from the gravitational pull of the Earth? What is its value?

9.If an object is at rest can you conclude that no force is acting on it?

10.While riding a bicycle, if you stop pedaling you will still continue to move forward. Why?

11.If a rope on which you are swinging on breaks when you are at the bottom of your swing, what will happen to you (describe the path you will take [fall])?

12.Consider an apple falling off a tree. What forces are acting?

13.Consider a large truck and a small car driving up a straight steep hill. The truck is moving at 90 km/hr and the car at 45 km/hr. Assuming that their speeds are constant, which of the two vehicles experiences a larger net force?

14.A car is moving down a straight steep hill. By applying the brake, the driver is able to keep the speed of the car constantly getting smaller. What do we know about the net force in this situation?

15.Suppose that a planet was discovered that has twice the mass and twice the diameter of the Earth. What would be the escape velocity for this planet?

16.Suppose that the Sun started shrinking in size, without losing any mass. What would be the effect of the Sun's changing size be on the orbits of the planets?

17.The acceleration of gravity on the Earth's surface is 9.8 m/s2. What is the acceleration of gravity at a height of 6,400 km above the Earth's surface?

18.What is the average orbital speed of the Earth around the Sun? (Note: r = 1.5  1011 m and P = 3.16  107s)

19.What did Newton's modification of Kepler's 3rd law allows astronomers to determine?

20.Mars completes one orbit around the Sun in approximately two Earth years. Mars orbits at an average distance to the Sun of about 1.5 AU, and Mars' mass is about 1/10 of the Earth's mass. In terms of the Earths orbital speed what would Mars' orbital speed be?

21. Calculate the escape velocity from the Earth, given that the mass of the Earth is 6 x 1024 kilograms and its radius 6 x 106 meters. In this problem, round off G to 7 x 10-11 meters3/(-s-2kg-1).

22. Calculate the escape velocity from the Sun, given that its mass is 2 x 1030 kg and its radius is 7 x 108 meters.

23. Which body has a larger escape velocity, Mars or Saturn? M Mars = 0.1 M Earth M Saturn = 95 M Earth R Mars = 0.5 R Earth R Saturn = 9.4 R Earth

24. Calculate your weight on the Moon.

25. Given that Jupiter is about 5 times farther from the Sun than the Earth (5 AU’s), calculate its orbital velocity. How many years does it take Jupiter to complete an orbit around the Sun?

26. Given that the mass of the Milky Way galaxy is 1011 times that of the Sun and that the Sun is 2.6 x 1020 meters from its center, what is the Sun's orbital speed around the center of the galaxy? How long does it take the Sun to orbit the Milky Way? (In this problem, we assume that the galaxy can be treated as a single spherical blob of matter. Strictly speaking, this isn't correct, but the far more elaborate math needed to calculate the problem properly ends up giving almost the same answer.)

27. A good baseball pitcher can throw a ball at 100 miles/hr (about 45 meters/s). If the pitcher were on the fictional asteroid Cochise, could the pitcher throw the ball fast enough so it would escape from Cochise? (Note: Assume Cochise is a sphere and that its mass is M = 9.6 x 1016 kg and its radius is 20 km = 2.0 x 104 meters.)

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