题目内容

A large crate of mass m is placed on the back of a truck but not tied down. As the truck accelerates forward with an acceleration a, the crate remains at rest relative to the truck. What force causes

A. the normal force
B. the force of gravity
C. the force of friction between the crate and the floor of the truck
D. the “ma” force
E. none of these

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An object that’s moving with constant speed travels once around a circular path. Which of the following is/are true concerning this motion？I. The displacement is zero. II. The average speed is zero. I

A. I only
B. I and II only
C. I and III only
D. III only
E. II and III only

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As a block slides down a frictionless incline, which of the following statements is true（）

A. Both its speed and acceleration increase
B. Its speed and acceleration remain constant
C. Its speed increases and its acceleration remains constant
D. Both its speed and acceleration decrease
E. Its speed increases and its acceleration decreases
F. None of these

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Which of the following is an example of a nonconservative force（）

A. gravity
B. magnetism
C. friction
D. none of the others

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A car is going around a racetrack at constant speed. The curves around the track have different radii. In which turn is the magnitude of the car’s acceleration the greatest（）

A. It is the greatest in the turn with the greatest radius
B. It is the greatest in the turn with the smallest radius
C. The acceleration is zero everywhere because of the constant speed
D. More information is needed to determine the answer
E. None of the others

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A large crate of mass m is placed on the back of a truck but not tied down. As the truck accelerates forward with an acceleration a, the crate remains at rest relative to the truck. What force causes

A. the normal force B. the force of gravity C. the force of friction between the crate and the floor of the truck D. the “ma” force E. none of these

An object that’s moving with constant speed travels once around a circular path. Which of the following is/are true concerning this motion？I. The displacement is zero. II. The average speed is zero. I

As a block slides down a frictionless incline, which of the following statements is true（）

Which of the following is an example of a nonconservative force（）

A car is going around a racetrack at constant speed. The curves around the track have different radii. In which turn is the magnitude of the car’s acceleration the greatest（）

A. the normal force
B. the force of gravity
C. the force of friction between the crate and the floor of the truck
D. the “ma” force
E. none of these