physics unit 3

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 ms. 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?

0.72 N

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.

1. Meterstick 2. Protractor

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. The toy experiences a component of the tension force toward the center of the circular path that serves as the centripetal force exerted on the toy. Which of the following measurements could a student use to determine the net centripetal force exerted on the toy? Select two answers.

1. Use a scale to determine the mass of the toy. Use a protractor to determine the angle θ between a vertical line and the angle that the string makes with the vertical line. 2. Use a stopwatch to determine the time for the toy to complete one revolution. Use a meterstick to measure the radius of the toy's circular path, R. Use a scale to determine the mass of the toy.

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?

15 N

A student rides a bicycle in a circle at a constant speed and constant radius. A force diagram for the student-bicycle system is shown in the figure above. The value for each force is shown in the figure. What is the acceleration of the student-bicycle system?

5 m/s^2

A cart of mass m is moving with speed v on a smooth track when it encounters a vertical loop of radius R, as shown above. The cart moves along the inside of the entire loop without leaving the track. All frictional forces are negligible. Which of the following free-body diagrams shows the force or forces exerted on the cart at point Q ?

Diagram with Fnormal and Fgravity

A ball is swung in a vertical circle such that at one point along its circular path the forces exerted on the ball can be represented by the free body diagram. The magnitude of the tension force exerted on the ball, T, is twice that of the force due to gravity exerted on the ball from Earth, Fg. What is the location of the ball, and what is the magnitude of the centripetal acceleration of the ball?

Location : Top of the Circle Acceleration : 3g

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?

Position C

An object of mass M1 travels in a circular path of radius R on a horizontal table. The object is attached to a string that passes through a hole in the center of the table. An object of mass M2 is attached to the other end of the string and hangs vertically under the table, which produces a force on M1. All frictional forces are considered to be negligible. Which quantity or quantities must be measured to determine the tangential speed required to keep the system in equilibrium?

R, M1, and M2

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?

The diagram that looks like a clock that reads 5:50

A moon orbits an isolated planet in deep space. Which of the following forces that the planet exerts on the moon can be considered as negligible?

The electric force

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?

The gravitational force between the astronaut and the asteroid

A student conducts an experiment in which a 0.5 kg ball is spun in a vertical circle from a string of length 1 m, as shown in the figure. The student uses the following equation to predict the force of tension exerted on the ball whenever it reaches the lowest point of its circular path at a known tangential speed for various trials. FTension= m * [ (v^2)/(r)] 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?

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 satellite of mass m orbits a moon of mass M in uniform circular motion with a constant tangential speed of v. The figure shows the net force exerted on the satellite by the moon and the direction of the tangential velocity of the satellite at time t0. Which of the following statements is true regarding the motion of the satellite?

The tangential velocity of the satellite does not remain constant.

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?

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

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

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

A ball of mass M is on a horizontal surface with negligible friction. One end of a string is attached to the ball so that it is spun in a horizontal circle of radius R at tangential speed v0, as shown in Figure 1. A free-body diagram for the ball at an instant in time is shown in Figure 2. The magnitude of the tension force is also indicated in Figure 2. Which of the following equations represents the centripetal acceleration of the ball if its tangential speed is increased to 2v0?

ac=(4(v0^2))/R

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 t0 is shown in Figure 3. What is the magnitude of the acceleration of the object of mass M at time t0?

g tan 0