A puck moves on a horizontal air table. It is attached to a string that passes through a hole in the center of the table
As the puck rotates about the hole, the string is pulled downward very slowly and shortens the radius of rotation, so the puck gradually spirals in towards the center. What happens to the puck's angular speed?
The tension in the string is directed towards the center, so there is no torque about the center. Thus, its angular speed has to increase to keep the angular momentum constant.
You might also like to view...
A solenoid 4.0 cm in radius and 4.0 m in length has 8 000 uniformly spaced turns and carries a current of 5.0 A. Consider a plane circular surface (radius = 2.0 cm) located at the center of the solenoid with its axis coincident with the axis of the solenoid. What is the magnetic flux through this surface? (1 Wb = 1 T × m2)
a. 63 mWb b. 16 mWb c. 0.25 mWb d. 10 mWb e. 5.0 mWb
One of the discoveries made by the Voyager probes while near Jupiter was
A) Io has a featureless surface that never changes. B) a thin ring of dust around the equator. C) the absence of a magnetic field around the giant planet. D) that the Great Red Spot is uniform and featureless. E) each of the four large moons produces a strong magnetic field.
The focal length of a convex mirror is
A. positive B. negative C. zero D. infinity
Which of the following statements about quantum tunneling is not true?
A) It is used in modern electronics and, in fact, our modern-day computers would not work without it. B) It plays a crucial role in nuclear fusion in the Sun. C) It allows electrons and other subatomic particles to pass through wall-like energy barriers even when it seems they do not have enough energy to get through the barriers. D) Although it has been observed to occur, it violates all other known laws of nature, and explaining it therefore represents a major challenge to physicists.