Elf- Arrow Lock

A ball attached to a string is whirled around in a horizontal circle having a radius r. If the radius of the circle is changed to 4r and the same centripetal force is applied by the string, the new speed of the ball is which of the following?

One-quarter the original speed

The same as the original speed

One-half the original speed

Four times the original speed

Twice the original speed

Buddy has a wooden box he first pulled across a horizontal steel plate as shown in diagram A. Then Buddy pulled the box across the same steel plate while the plate was inclined as shown in diagram B.

Compare the force required to overcome friction in each case.

the frictional force is the same in both cases

the inclined case has a greater frictional force

the inclined case has less frictional force

the frictional force increases with angle until the angle is 900, then drops to zero

8.5 x 103 N

5.8 x 10-8 N

What is the gravitational force acting on a 59-kg person due to another 59-kg person standing 2.0 m away? We can model each person as a small sphere.

1.2 x 10-7 N

9.8 x 10-10 N

2.0 x 10-9 N

Pulling out of a dive, the pilot of an airplane guides his plane into a vertical circle with a radius of 600m. At the bottom of the dive, the speed of the airplane is 150 m/s. What is the apparent weight of the 70-kg pilot at that point?

2600 N

690 N

3300 N

1400 N

490 N

The horizontal turntable shown above rotates at a constant rate. As viewed from above, a coin on the turntable moves counterclockwise in a circle as shown.

Which of the following vectors best represents the direction of the frictional force exerted on the coin by the turntable when the coin is in the position shown?