第三章单元测试
- 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.) ( )
- 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 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? ( )
- 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? ( )
Consider a box that is placed on different surfaces. In which situation(s) is there no friction force acting on the box? ( )
A:easier B:just as easy C:harder D:More information is needed to determine
答案:just as easy
A:It increases with increasing distance from the earth. B:This information by itself isn’t enough to answer the question. C:It is the same at all distances from the earth. D:It decreases with increasing distance from the earth.
A: B: C: D:
A:The elevator is now speeding up. B:The elevator now decelerates and rises C:The elevator is now speeding down. D:The elevator now rises up at a constant speed
A: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. B:The box is at rest on a rough tilted surface. C: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. D: The box is at rest on a rough horizontal surface.
温馨提示支付 ¥3.00 元后可查看付费内容,请先翻页预览!