Module 7 review questions Flashcards
An object moves at constant speed. Is the acceleration necessarily zero? Why or why not?
The acceleration is not necessarily zero. In circular motion, the speed is constant, but because the direction is always changing, the velocity changes.
Consider an object moving uniformly in a circle. If the speed of the object suddenly doubles, but the radius of the motion does not change, what new centripetal acceleration is needed to keep the object moving in a circle?
The centripetal acceleration quadruples.
A student places two objects on a table only a few centimeters apart. The student says that since the objects do not move towards one another, there must not be any gravitational force between the two objects. Is the student correct? Why or Why not?
The student is incorrect. The objects do not move towards one another because, in this case, gravity is not strong enough to overcome friction.
Newton’s Third Law states that for every action there is an equal and opposite reaction. Suppose two massive objects sit close to one another. The first object exerts a gravitational force on the second object. What is the equal and opposite force that exists in reaction to this gravitational force?
The reaction force is the gravitational force that the second object exerts on the first.
You have already been told that the acceleration due to gravity is not really constant near the surface of the earth. It varies a bit depending on where you are. Compare the acceleration due to gravity at sea level to that at the tip of Pike’s Peak. Where do you expect the acceleration due to gravity to be greater?
Gravitational force decreases the farther you are away from the center of the earth. Thus, the gravitational acceleration will be greater at sea level.
Two objects are in close proximity to one another. If the distance between them is suddenly doubled, what happens to the strength of their mutual gravitational attraction?
The gravitational force decreases by a factor of 4.
An annoying fly travels around your head in a circle. If the fly suddenly increases its speed but stays in the same circle, does the fly’s orbital period increase or decrease?
Its orbital period decreases and its orbital frequency increases.
In the spin cycle of an automatic washing machine, the clothes are spun around inside the machine at a high rate of speed. This removes a large amount of the water that has soaked into the clothes. Given the fact that the walls of the washing machine have small holes in them, explain the physics behind why this works.
The water and the clothes have a velocity tangent to the circle in which they spin. To keep them spinning in a circle, the walls of the washing machine push on the clothes, providing a centripetal force. However, the water in the clothes might hit one of the holes in the wall rather than the wall itself. If that happens, no centripetal force can be applied to the water, and it continues traveling tangent to the circle, going through the hole and into the drain.
