Version PREVIEW – HW25, centripetal forces – gleue – (99999-99)
This print-out should have 12 questions.
Multiple-choice questions may continue on
the next column or page – find all choices
before answering.
Centripetal Acceleration
001 10.0 points
A car rounds a curve while maintaining a
constant speed.
Is there a net force on the car as it rounds
the curve?
1. It depends on the sharpness of the curve
and speed of the car.
2. No – its speed is constant.
3. Yes. correct
A
B
C
D
1
E
If these events are observed from directly
above, which path would the ball most closely
follow after the string breaks?
1. (B) correct
2. (A)
3. (C)
Conceptual 04 Q05
002 10.0 points
A passenger on a Ferris wheel moves in a
vertical circle at constant speed.
Are the forces on her balanced?
1. No; the direction of net force does not
change.
2. Yes; the speed is constant.
3. Yes; it moves in a vertical circle.
4. No; there is an inward net force. correct
Rotating String Breaks
003 10.0 points
A steel ball is attached to a string and is
swung in a horizontal circular path as illustrated in the figure. At point P , the string
suddenly breaks near the ball.
4. (E)
5. (D)
Rock in a Horizontal Circle 02
004 10.0 points
You’ll need to find the mass of the rock first.
A string under a tension of 75 N is used to
whirl a rock in a horizontal circle of radius
3.2 m at a speed of 29.93 m/s. The string is
pulled in, and the speed of the rock increases.
When the string is 0.43 m long and the speed
of the rock is 57.9 m/s, the string breaks.
What is the breaking strength of the string?
Correct answer: 2088.75 N.
Conical Pendulum 05
005 10.0 points
Consider a conical pendulum, where a
string with length ℓ is attached to a mass
m. The angle between the string and the vertical is θ. The orbit is in the horizontal plane
with radius r and tangential velocity ~v.
Version PREVIEW – HW25, centripetal forces – gleue – (99999-99)
component of tension that acts centripetally.
For this problem, you’ll have to get the radius. Draw a force diagram. You’ll generate
two equations (vertical and horizontal) and
substitute. Your masses will cancel out and
you can find the velocity in meters/second.
A small metal ball is suspended from the
ceiling by a thread of negligible mass. The
ball is then set in motion in a horizontal circle
so that the thread describes a cone.
The acceleration of gravity is 9.8 m/s2 .
θ
g
ℓ
r
2
v
m
What is the free body diagram for mass m?
The acceleration of gravity is 9.8 m/s2 .
2. 4
◦
31
9.8 m/s2
θ
m
1.
v
6.6 kg
What is the speed of the ball when it is in
circular motion?
θ
2.
Correct answer: 2.6979 m/s.
007 (part 2 of 2) 10.0 points
How long does it take Tperiod for the ball to
rotate once around the axis?
θ
3.
correct
θ
4.
θ
5.
Conical Pendulum 02
006 (part 1 of 2) 10.0 points
Remember for conical pendulums, there is a
Correct answer: 2.87876 s.
Hammer Throw
008 (part 1 of 2) 10.0 points
The centripetal acceleration (ac) =
v(squared)/r. But the velocity = (omega*r).
Make sure the omega is in radians/second.
For part 2, m*ac = Fc.
Assume: The length of the athlete’s arm
is included in the length given for the chain
below.
An athlete whirls a(n) 8.56 kg hammer tied
to the end of a(n) 1.4 m chain in a horizontal
circle. The hammer moves at the rate of
1.25 rev/s.
What is the centripetal acceleration of the
hammer?
Version PREVIEW – HW25, centripetal forces – gleue – (99999-99)
Correct answer: 86.359 m/s2 .
009 (part 2 of 2) 10.0 points
What is the tension in the chain?
Correct answer: 739.233 N.
Conceptual 05 14
010 10.0 points
Make sure the average distance (radius) is
converted to meters from km. First find the
velocity using circumference over the orbital
time; then use the centripetal equation to get
your force. In this case, the centripetal force
is supplied by gravity.
Calculate the centripetal force exerted on
the Earth by the Sun. Assume that the period
of revolution for the Earth is 365.25 days,
the average distance is 1.5 × 108 km and the
Earth’s mass is 6 × 1024 kg.
1. 7.24562 × 1020 N
2. 4.6238 × 1029 N
3. 2.66331 × 1032 N
4. 3.56775 × 1019 N
5. 1.28439 × 1026 N
6. 7.24562 × 1022 N
7. 1.62932 × 1021 N
8. None of these
9. 3.56775 × 1022 N correct
Holt SF 07Rev 43
011 (part 1 of 2) 10.0 points
Use 9.81 m/s/s for g. Use ac=v(squared)/r
to find the radius on part 1. On part 2 the
net force = Fc= m*ac. Make sure to use 9.81
m/s/s for g.
An airplane is flying in a horizontal circle
at a speed of 101 m/s. The 70.0 kg pilot
does not want the centripetal acceleration to
exceed 6.37 times free-fall acceleration.
3
a) Find the minimum radius of the plane’s
path.
Correct answer: 163.243 m.
012 (part 2 of 2) 10.0 points
b) At this radius, what is the magnitude of
the net force that maintains circular motion
exerted on the pilot by the seat belts, the
friction against the seat, and so forth?
Correct answer: 4374.28 N.