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Circular Motion & Gravity Test 2011
1/21/11
Honors Physics
Period____
E. Burns
1] A ball on the end of a string is swung in a vertical circle. The mass of the ball is 0.25kg and the radius of the circle r =
0.75 meters. The position of the ball is marked every quarter of a revolution in the diagram below.
1
4
2
3
a) On the diagram, draw all of the forces acting on the ball when it is at position #4. Be sure to label each force
b) If the speed of the ball at position #3 is 5 m/s, calculate the tension force in the string as the ball passes
through position #3.
c) When the ball is at position #4, the tension force on the string is twice as great as the weight of the ball.
Suppose the string breaks just as the ball is at position #4, how high will the ball go after the string breaks?
2] Lab Practical: The flying pig is suspended from the ceiling by a thin string. Find the period of the pig using
only a meterstick. Record your data and calculations in the space below.
3] Suppose that the combined mass of you and your bike is 75kg. You are riding down the street and have to make a turn
in a circular section of road whose radius is approximately 6.5 m. The speedometer on your bike reads 20 km/hr. If the
coefficient of static friction between your tires and the road is 0.79, are you going too fast to make the turn safely? Show
all your work and justify your answer.
Part B: Multiple Choice
1. Consider a point on a bicycle wheel as the wheel turns about a fixed axis, neither speeding up nor slowing
down. Compare the linear and centripetal accelerations of the point.
a Both are zero.
b Only the centripetal acceleration is zero.
c Only the linear acceleration is zero.
d Neither is zero.
2. Which has greater linear speed, a horse near the outside rail of a merry-go-round or a horse near the inside
rail?
a The inside horse
b The outside horse
c Neither—they both have the same linear speed.
3. "Centrifugal forces" are an apparent reality to observers in a reference frame that is
a rotating.
b an inertial reference frame.
c moving at constant velocity.
d at rest.
e none of the above
4. If you whirl a tin can on the end of a string and the string suddenly breaks, the can will
a fly directly away from you.
b fly off, tangent to its circular path.
c fly directly toward you.
d spiral in toward your hand.
e spiral away from your hand.
5. A car travels in a circle with constant speed. The net force on the car
a is zero because the car is not accelerating.
b is directed forward, in the direction of travel.
c is directed toward the center of the curve.
d none of the above
6. What provides the centripetal force that keeps the moon in orbit around the earth?
a. normal force
b. weight
c. friction
d. tension