An air puck of mass 0.034 kg is tied to a string and allowed to revolve in a circle of radius 1.7m on a frictionless horizontal surface. The other end of the string passes through a hole in the center of the surface, and a mass of 2.5 kg is tied to it, as shown. The suspended mass remains in equilibrium while the puck
revolves on the surface.
1.7 m
2.5 kg
0.034 kg
What is the magnitude of the force that
maintains circular motion acting on the puck?
The acceleration due to gravity is 9.81 m/s
2
.
Answer in units of N.

Arunner is jogging at a steady 3.6 km/hr. when the runner is 2.9 km from the finish line, a bird begins flying from the runner to the finish line at 14.4 km/hr (4 times as fast as the runner). when the bird reaches the finish line, it turns around and flies back to the runner. even though the bird is a dodo, we will assume that it occupies only one point in space, i.e., a zero-length bird. how far does the bird travel? (b) after this first encounter, the bird then turns around and flies from the runner back to the finish line, turns around again and flies back to the runner. the bird repeats the back and forth trips until the runner reaches the finish line. how far does the bird travel from the beginning? (i.e. include the distance traveled to the first encounter)