C  2r
1.
v
T
ac 
r
F  mac  m
v2
r
In our physics class, circular motion is always calculated assuming a constant speed. Yet velocity
( a word we use often instead of speed) is not constant. Why is velocity not constant?
a.
b.
c.
d.
2.
Circular Motion Final exam Review
2r
v2
Speed is not a component of velocity
Speed is constant but direction is changing
Velocity is a vector that involves more than just speed.
Both b and c are correct.
You want to make a bowling ball travel in a circular counter-clockwise path around you (this
means YOU are the center point). After you set the ball in motion “to the left”, in what direction
will force need to be exerted to keep the ball in a circular path?
a. You need to constantly push the ball away from you
b. You need to constantly push the ball toward you.
c. You need to constantly push the ball to the left
3.
When referring to circular motion, a period is
a. The distance traveled in one revolution
b. The time required to travel one revolution
c. The distance that you can travel in a second
4.
When walking in a circle counterclockwise you are
a. Pushing toward the center of your path with your right foot
b. Pushing toward the center of your path with your left foot
c. Exerting equal force with both feet.
5.
Besides gravity (which pushes down on you) and the normal force (pushing up on you), what
force is being used to keep you on a circular path?
a. Inertia
b. Friction
c. Centrifugal force
6.
We use the formula 2r for distance because this formula will give us
a. The distance around the circle
b. The diameter of the circle
c. The volume of the circle.
7.
Velocity is defined as
a. Circumference divided by frequency (Circumference/frequency)
b. Radius multiplied by Period (Radius*Period).
c. Circumference divided by Period (Circumference/Period)
8.
If you travel around a circle that has a radius of 2 meters in 2 seconds, the distance that you
traveled is
a. ~12.5 meters
a.
0 meters
b.
25 meters
c.
6.25 meters
9.
If you are traveling in a circle at constant speed, are you accelerating?
a. Yes, because you are changing your speed
b. Yes, because you are changing direction
c. No, because you are traveling in a circular path (which is really a straight line).
10. Acceleration which points to the center of a circular path is called
a. Centrifugal force
b. Inertia
c. Centripetal acceleration
11. Consider the following picture. If you traveled at the same average speed around each of the
circles, the period would be
a. shorter for the larger circle
b. shorter for the smaller circle
The direction of a velocity vector at every instant is tangential to the circle.
This means that unless some force is applied to the object, it will not continue
to travel in a circle. It wants to “go straight” due to inertia. When we measure
velocity, we are really estimating linear velocity at the “edge” of the circle. As
the object turns, the direction of linear speed changes, thus we have changing
speed but not direction. So based on what you know…answer the question on
the next page:
12. A tube is been placed upon the table and shaped into a three-quarters circle. A golf ball is pushed
into the tube at one end at high speed. The ball rolls through the tube and exits at the opposite end.
Draw an arrow to show what direction the ball will travel in as it exits the tube.
13. What two things MUST be true for velocity to be constant?
a. Speed and acceleration must be constant
b. Speed and direction must be constant
c. Speed must be constant and acceleration must be zero
d. Either c or b is correct
The acceleration of an object is often measured using a device known as an accelerometer. A simple
accelerometer consists of an object immersed in a fluid such as water. Consider a sealed jar which is
filled with water. A cork attached to the lid by a string can serve as an accelerometer.
To test the direction of acceleration for an object moving in a circle, the jar can be inverted and
attached to the end of a short section of a wooden 2x4. A second accelerometer constructed in the
same manner can be attached to the opposite end of the 2x4. If the 2x4 and accelerometers are
clamped to a rotating platform and spun in a circle, the direction of the acceleration can be clearly
seen by the direction of lean of the corks.
14. Which direction will the corks lean?
a. They will lean inward toward the center of the circle
b. They will lean outward away from the circle
c. They will remain “straight up and down
15. The direction in which the corks move demonstrates
a. Centripetal force
b. Centrifugal force
c. Constant velocity and a net force of zero.
16. The flames would move inward toward the center.
17. Answer the following:
e.
Acceleration: Yes or No? Explain.
Yes, the velocity changes
If there is an acceleration, then what direction is it?
To the left.
18.
Known Information:
Requested Information:
m = 900 kg
a = ????
v = 10.0 m/s
Fnet = ????
R = 25.0 m
a = v2 / R
Fnet = m • a
Solve the problem. a= 4 m/s/s
F=3600 N
19. What equation will you use to solve for v? Write the equation then solve the problem.
V = 10 m/s
20. What equation will you use to solve for a? Write the equation then solve the problem.
a = v2/r
a = (100m2/s2)/(25 m) = 4 m/s/s
21. What equation will you use to solve for Fnet? Write the equation then solve the problem.
Fnet = m • a
F = (900kg)(4 m/s/s)= 3600 N
22. Anna Litical is practicing a centripetal force demonstration at home. She fills a bucket with water, ties
it to a strong rope, and spins it in a circle. Anna spins the bucket when it is half-full of water and when it is
quarter-full of water. In which case is more force required to spin the bucket in a circle? Explain using an
equation as a "guide to thinking."
Half-full because a change in mass results in the same change in the amount of force if the acceleration
is constant.
23. A Lincoln Continental and a Yugo are making a turn. The Lincoln is four times more massive
than the Yugo. If they make the turn at the same speed, then how do the centripetal forces acting
upon the two cars compare. Explain.
It will quadruple the force Lincoln requires 4 times the force of the Yugo because of
the Lincoln has 4 times the mass.
24. The Cajun Cliffhanger at Great America is a ride in which occupants line the perimeter of a
cylinder and spin in a circle at a high rate of turning. When the cylinder begins spinning very
rapidly, the floor is removed from under the riders' feet. What affect does a doubling in speed have
upon the centripetal force? Explain.
Quadruple the force. Doubling the speed results in the acceleration increasing by
4 times, so the force increases by the same factor.
25. Determine the centripetal force acting upon a 40-kg child who makes 10 revolutions around the
Cliffhanger in 29.3 seconds. The radius of the barrel is 2.90 meters.
T = 2.93 s
F = ma = (40 kg)(13.3 m/s/s)= 532.895 N