University physics答案2023秋

第三章测试

1.Suppose an astronaut landed on a planet where g=19.6 m/s². Compared to earth, would it be for her to catch a ball that is moving horizontally at 12 m/s? (Assume that the astronaut’s spacesuit is a lightweight model that doesn’t impede her movements in any way.) （ ）
A:harder B:easier C:just as easy D:More information is needed to determine
答案:C
2.Satellites are held in orbit by the force of our planet’s gravitational attraction. A satellite in a small-radius orbit moves at a higher speed than a satellite in an orbit of large radius. Based on this information, what you can conclude about the earth’s gravitational attraction for the satellite? （ ）
A:It increases with increasing distance from the earth. B:It is the same at all distances from the earth. C:It decreases with increasing distance from the earth. D:This information by itself isn’t enough to answer the question. 3.A traffic light of weight w hangs from two lightweight cables, one on each side of the light. Each cable hangs at a 45° angle from the horizontal. What is the tension in each cable? （ ）
A: B: C: D: 4.The person in the elevator holds a spring scale with a heavy object. Now the reading of the spring scale suddenly becomes larger (The person never moves). What is the movement of the elevator at this time? （ ）
A:The elevator is now speeding up. B:The elevator now rises up at a constant speed C:The elevator is now speeding down. D:The elevator now decelerates and rises 5.

Consider a box that is placed on different surfaces. In which situation(s) is there no friction force acting on the box? (     )

A: The box is at rest on a rough horizontal surface.  B:The box is on the rough-surfaced flat bed of a truck—the truck is moving at a constant velocity on a straight but tilted road, and the box remains in the same place in the middle of the truck bed. C:The box is on the rough-surfaced flat bed of a truck—the truck is speeding up on a straight, level road, and the box remains in the same place in the middle of the truck bed.  D:The box is at rest on a rough tilted surface.