PHYSICS

HOMEWORK SET 4

Due 6/24

1. To tighten a spark plug, it's recommended that a torque of 15 N m be applied. If a mechanic tightens the spark plug with a wrench that is 25 cm long, what is the force needed? Remember t = r F

2. A bowling trophy of mass 1.61 kg is held at arm's length, a distance of 0.65 m from the shoulder joint. What torque does the trophy exert about the shoulder if the arm is horizontal?

3. A person holds a ladder horizontally at its center. Treating the ladder as a uniform rod of length 3.15 meter and mass of 8.42 kg, find the torque the person must exert on the ladder to give it an angular acceleration of 0.302 radians/sec2.

4. A fish takes the bait and pulls on the line with a force of 2.2 N. The fishing reel, which rotates without friction, is a cylinder of radius 0.055 m and mass of 0.99 kg. What is the angular acceleration of the fishing reel?

5. A uniform crate with a mass of 16.2 kilograms rests on the floor with a coefficient of friction of m = 0.571. The crate is a uniform cube with sides 1.21 meters in length. What horizontal force applied to the top of the crate will start the crate to tip?

6. Calculate the angular momentum of the Earth around its own axis due to its daily motion. Assume a sphere with uniform density.

7. As an ice skater begins a spin, his angular speed is 3.17 rad/s. After pulling in his arms, his angular speed increases to 5.46 rad/s. Find the ratio of the skater’s final moment of inertia to his initial moment of inertia.

8. How much work must be done to accelerate a baton from rest to an angular speed of 7.4 rad/s about its center? Consider the baton to be a uniform rod of length 0.53 m and a mass of 0.44 kg.

9. A 6.1-kg bowling ball and a 7.2-kg bowling sphere rest on a rack 0.75 m apart.

a. What is the force of gravity on each of the spheres by the other one?

b. At what distance is the force of gravity between the spheres equal to 2.0 x 10-9 N?

10. At a certain distance from the center of Earth, a 4.6-kg object has a weight of 2.2 N.

Find the distance.

11. Find the orbital speed of a satellite in a geosynchronous circular orbit 3.58 x 107 m above Earth's surface.

12. Phobos, a moon of Mars, orbits at a distance of 9378 km from the center of Mars. What's its orbital period?

13. A satellite orbits the Earth in a circular orbit of radius r. At some point its rocket engine his fired in such a way that its speed increases rapidly by a small amount. As a result,

a. does the apogee distance increase, decrease, or stay the same?

b. does the perigee distance increase, decrease, or stay the same?

14. Find the speed of the binary stars Centauri A and Centauri B. They are separated by a distance of 3.45 x 1012 m and they have an orbital period of 2.52 x 109 seconds (that's about 80 years). They have the same mass. (Binary stars are near each other and orbit each other).

15. Find the Escape Velocity, vesc, for the planet Mercury.

END

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