20 Review Questions for C3T1

A satellite is a large distance from a planet, and the gravitational force from the planet is the only significant force exerted on the satellite. The satellite begins falling toward the planet, eventually colliding with the surface of the planet. As the satellite falls, which of the following claims is correct about how the force that the planet exerts on the satellite Fps changes and how the force that the satellite exerts on the planet Fsp changes, if at all? What reasoning supports this claim?

a) Fps and Fsp both increase. The gravitational forces that two objects exert on one another decrease as the separation between the objects increases, and these forces are always equal in magnitude.

A 2 kg object is a distance of 10,000,000 m away from the center of Earth, which has a mass of nearly 6 × 10^24 kg. What is the approximate gravitational field strength of Earth's gravitational field at the location of the 10 kg object?

4 N/kg

A student must design an experiment to determine the gravitational mass of an object. Which of the following experiments could the student use? Select two answers.

a) Place the object on one side of a lever at a known distance away from a fulcrum. Place known masses on the other side of the fulcrum so that they are also placed on the lever at known distances from the fulcrum. Move the known masses to a known distance such that the lever is in static equilibrium. AND d) Place the object on the end of a vertically hanging spring with a known spring constant. Allow the spring to stretch to a new equilibrium position, and measure the distance the spring is stretched from its original equilibrium position.

An object is thrown upward with a speed of 20 m/s near the surface of a planet where the gravitational field strength is a constant magnitude of 6 N/kg. The vertical position versus time of the object is shown in the graph. Is the object considered to be in free fall?

a) Yes, because the only force exerted on the object is the force due to gravity from the planet.

One end of a string is attached to the ceiling with the other end attached to a toy. The toy can be set into motion such that it travels in a horizontal circular path at a constant tangential speed, as shown above. Which of the following measuring tools, when used together, could be used to determine the time it takes for the toy to complete one revolution around the circle? Select two answers.

a) protractor AND b) meterstick

During an experiment, an object is placed on a disk that rotates about an axle through its center, as shown in Figure 1. The disk is a distance R=0.10 m from the center and rotates with a constant tangential speed of 0.60 m/s. A free body diagram of the forces exerted on the block is shown in Figure 2 with an unknown force of friction. What is the force of friction exerted on the object?

b) 0.72 N

A ball is attached to one end of a string such that the ball travels in a vertical circular path near Earth's surface. The force diagram of the ball at its lowest point in the circular path is shown above. What is the net centripetal force exerted on the ball?

b) 15 N

An object is released from rest near the surface of a planet. The vertical position of the object as a function of time is shown in the graph. All frictional forces are considered to be negligible. The strength of the gravitational field is most nearly

b) 6 N/kg

A student must determine the inertial mass of a block that is pulled across a horizontal surface using a force probe and an accelerometer. The student's data are represented in the graph above. What must the student do to determine the inertial mass of the block?

b) Calculate the slope.

One end of a string is attached to a vertical pole with the other end of the string attached to a ball that swings in a horizontal circular path, as shown. Which of the following free body diagrams represents the forces exerted on the ball?

b) Full body diagram with one arrow pointed to the top left and down.

A planet travels in an elliptical path around a star, as shown in the figure. As the planet gets closer to the star, the gravitational force that the star exerts on the planet increases. Which statement of reasoning best supports and correctly identifies what happens to the magnitude of the force that the planet exerts on the star as the planet gets closer to the star?

b) The force increases because it is part of a Newton's third law pair of forces with the force that the star exerts on the planet.

A moon of mass 1 x 10^20 kg is in a circular orbit around a planet. The planet exerts a gravitational force of 2 x 10^21 N on the moon. The centripetal acceleration of the moon is most nearly?

c) 20 m/s^2

A 10kg object is near a planet's surface such that the gravitational field strength is 4 N/kg. With what force is the planet attracted to the 10kg object?

c) 40 N

A satellite of mass 1000 kg is in a circular orbit around a planet. The centripetal acceleration of the satellite in its orbit is 5 m/s^2. What is the gravitational force exerted on the satellite by the planet?

c) 5000 N

A spaceship travels from a planet to a moon and passes through the three positions A, B, and C, shown above. Position B is midway between the centers of the planet and the moon. The planet has a larger mass than the moon. At which location could the net gravitational force exerted on the spaceship be approximately zero?

c) Position C

An object is dropped near the surface of a planet such that the gravitational field at the object's location is 8 N/kg. If the object is thrown upward at a speed of 20 m/s, what is the position of the object in relation to the position in which the object was released and thrown upward after 3s?

d) 24 m above the release position

An astronaut stands on the surface of an asteroid. The astronaut then jumps such that the astronaut is no longer in contact with the surface. The astronaut falls back down to the surface after a short time interval. Which of the following forces CANNOT be neglected when analyzing the motion of the astronaut?

d) The gravitational force between the astronaut and the asteroid

When the experiment is conducted, the student uses a force probe to measure the actual force of tension exerted on the ball. Why is the predicted force of tension different than the actual force of tension?

d) The student did not account for the downward force due to gravity at the ball's lowest point along its circular path, so the predicted force of tension is the net centripetal force exerted on the ball.

A comet passes by a planet with a speed Vo such that the comet travels in a straight line at the instant shown in the figure. The comet's tangential acceleration, centripetal acceleration, and force due to gravity from the planet at this location are provided in the table. Astronomers observe that the comet continues to travel in a nearly straight line, even though calculations show that the gravitational force exerted by the planet should cause the comet to move in a circular orbit. Why does the comet not travel in a circular path around the planet after the instant shown in the figure?

d) There must be another object such that the gravitational forces exerted on the comet are balanced at this location.

A solid disk of diameter D spins counterclockwise about its center at a constant speed. One end of a string of length l is attached to the edge of the disk with the other end attached to an object of mass M. At time t0, as the disk spins, the string makes an angle θ with respect to the vertical, as shown in Figure 1. A force diagram of all of the forces exerted on the object at time t0 are shown in Figure 2. The direction of the centripetal acceleration of the object at t0t0 is shown in Figure 3. What is the magnitude of the acceleration of the object of mass M at time t0?

d) g tanθ