Circular Motion, Planets, and Gravity
Select the best possible answer.
1. A car travels around a curve with constant speed. Does the velocity of car change in this process?
a. No, since the car travels with constant speed at all times, its velocity remains unchanged.
b. Yes, even though the speed remains constant but the direction of motion changes.
c. No, because for traveling around a curved path, the velocity must remain constant.
d. Yes, because at any moment the velocity vector must be directed toward the center.
2. A ball on the end of a string is whirled with constant speed in a counterclockwise horizontal circle. At point A the string breaks. Which of the curves sketched below represents the path the ball will take?
a. Path 1.
b. Path 2.
c. Path 3.
d. Path 4.
3. In the previous question, before the string breaks, what is the direction of the net force acting on the ball?
a. The net force is along the string and directed radially outward (away from the center).
b. The net force is along the string and is directed radially inward (toward the center).
c. The net force is directed along the direction of motion, tangent to the path of the ball.
d. There is not net force acting on the ball before the string breaks.
4. A car travels around a flat (non-banked) curve with constant speed. What is the direction of the net force acting on the car?
a. The force is directed along the radius toward the center of the curve.
b. The force is directed along the radius away from the center of the curve.
c. The force is directed along the direction of motion of the car.
d. The force is directed in the opposite direction of motion of the car.
5. How did Kepler's view of the solar system differ from that of Copernicus?
a. Kepler assumed that the planetary orbits are elliptical while Copernicus considered the orbits to be perfectly circular.
b. Kepler assumed that the planetary orbits are circular while Copernicus considered the orbits to be elliptical.
c. Kepler assumed a geocentric model for the planets while Copernicus considered a heliocentric model.
d. Kepler assumed the planets move around the epicycles while Copernicus considered the orbits to be elliptical.
6. Does the sun exert a larger force on the earth than that exerted on the sun by the earth?
a. The sun applies a larges force.
b. The earth applies a larger force.
c. The forces are the same.
d. The earth's force on the sun actually is zero.
7. A woman standing on the surface of the Earth has a mass of 70 kilograms and a weight of 686 N. If instead she were floating freely inside a non-rotating space habitat far from the Earth, her mass would be:
a. Less than 70 kg.
b. 70 kg.
c. More than 70 kg.
d. Zero.
8. In the previous question, the weight of the woman would be:
a. Less than 686 N.
b. 686 N.
c. More than 686 N.
d. Zero.
9. A 400-N person stands on the surface of the Earth. If he were somehow able to stand on a ladder so that he was twice as far from the center of the Earth, he would weight:
a. 0 N.
b. 100 N.
c. 200 N.
d. 400 N.
10. Referring to previous question; this would be because:
a. He would be above the atmosphere.
b. His mass would be the same wherever he was.
c. Gravitational force obeys an inverse square law.
d. Gravitational force is directly proportional to distance.
11. According to Kepler's laws, the paths of planets about the sun are
a. Parabolas.
b. Circles.
c. Straight lines.
d. Ellipses.
12. The Earth and the moon are attracted to each other by gravitational force. The larger Earth attracts the smaller moon with a force whose magnitude is:
a. Smaller than that of the force which the moon exerts on the Earth.
b. Greater than that of the force which the moon exerts on the Earth.
c. The same as that of the force, which the moon exerts on the Earth.
13. Referring to previous question; this is in accordance with:
a. The law of inertia
b. The conservation of energy
c. The fact that both moon and Earth orbit about a common point, the center of mass
d. The law of action and reaction.
14. According
to
a. Less the gravitational force between them.
b. Greater the gravitational force between them.
c. Greater the force between them by the square of the masses.
d. Greater the force between them by the square root of the masses.
15. According
to
a. Divides by 2 the gravitational force between them.
b. Multiplies by 2 the gravitational force between them.
c. Divides by 4 the gravitational force between them.
d. Multiples by 4 the gravitational force between them.
16. What is the force of gravity on a 500-newton woman standing on the Earth's surface?
a. 50 N.
b. 250 N.
c. 500 N.
d. 509.8 N.
17. An asteroid exerts a 360-N gravitational force on a nearby spacecraft. This force is directed:
a. Toward the asteroid.
b. Away from the asteroid.
c. Toward the sun.
d. None of the above.
18. How far must one travel to get away from the Earth's gravitational field?
a. To a region above the Earth's atmosphere.
b. To a region well beyond the moon.
c. To a region beyond the solar system.
d. Forget it; you can't travel far enough.
19. Three equal masses are located as shown in the diagram. What is the direction of the net force acting upon mass m2?
a. The net force is actually zero.
b. The net force is directed toward mass m1.
c. The net force is directed toward mass m3.
d. The net force is along a line perpendicular to the dashed line connecting the masses.
20. Are Kepler's laws valid for artificial satellites orbiting the earth?
a. Yes; Kepler's laws are valid for all planetary systems including the earth satellites.
b. Yes; however, it is only valid if the satellites are far away from the earth.
c. No; Kepler's laws are only valid for the planets orbiting the sun.
d. No; Kepler's laws are not valid for artificial satellites.
21. Are we normally able to see the new moon?
a. Yes; actually we see the entire surface of the moon facing the earth.
b. No; the face of the moon toward the earth is not illuminated.
c. Yes; during the new moon, the moon appears as a half circle.
d. No; usually during the new moon, clouds prevent us from seeing the moon.