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SOL PHYSICS 2016-2017
PH 5-8 Review Packet
Concepts
Equations
2𝜋𝑟
𝑇
1) Velocity is tangential to circular
motion.
𝑣𝑡 =
2) Centripetal acceleration and
Centripetal force are centerseeking
𝑎𝑐 =
3) Centripetal force is never its own
force (it will always be another
force as normal, tension, friction,
or gravity)
4) Centrifugal force is a pseudoforce that exists only to create a
balanced FBD (Centrifugal force
is really only inertia)
Hints (for 3x5 Note
cards)
𝑇=
𝑣2
𝑟
𝐺𝑀
𝑟2
4𝜋 2 𝑟
𝑎𝑐 = 2
𝑇
Top: 𝐹𝑁 , 𝐹𝑇 =
𝑚𝑣 2
𝑟
− 𝑚𝑔
Bottom: 𝐹𝑁 , 𝐹𝑇 =
𝑚𝑣 2
𝑟
5) Gravity is a field force generated
from mass.
2𝜋𝑣𝑡
𝑇
𝑎𝑐 =
𝐹𝑐 = 𝑚𝑎𝑐
𝑚𝑣 2
=
𝑟
𝑔=
𝑡𝑖𝑚𝑒
# 𝑜𝑓 𝑐𝑦𝑐𝑙𝑒𝑠
+ 𝑚𝑔
𝐹𝑔
𝐺𝑀
𝑣𝑜 = √
𝑟
𝑀𝑚
=𝐺 2
𝑟
𝑇=
𝑟=
2𝜋𝑟
√𝐺𝑀
𝑟
𝐺𝑀
𝑀𝑚
= √𝐺
2
𝑣𝑜
𝐹𝑔
R=distance from
surface + radius of
planet, sun, etc.
G = 6.673 x 10-11(N•m2)/kg2
Body’s Radius
Body’s Mass
Earth’s Radius: 6.37 x 106 m
Earth’s Mass: 5.98 x 1024 kg
Orbit: 1.50 x 1011 m
Moon’s Radius: 1.74 x 106 m
Moon’s Mass: 7.35 x 1022 kg
Orbit: 3.85 x 108 m
Sun’s Radius: 6.96 x 108 m
Mass: 1.99 x 1030 kg
1)
A 0.015-kg ball is shot from the plunger of a pinball machine. Because of a centripetal force of
0.028 N, the ball follows a circular arc whose radius is 0.25 m. What is the speed of the ball?
2)
In a skating stunt known as "crack-the-whip," a number of skaters hold hands and form a straight
line. They try to skate so that the line rotates about the skater at one end, who acts as the pivot. The
skater farthest out has a mass of 80.0 kg and is 6.10 m from the pivot. He is skating at a speed of 6.80 m/s.
Determine the magnitude of the centripetal force that acts on him
3)
At an amusement park there is a ride in which cylindrically shaped chambers spin around a
central axis. People sit in seats facing the axis, their backs against the outer wall. At one instant the outer
wall moves at a speed of 3.2 m/s, and an 83-kg person feels a 560-N force pressing against his back. What
is the radius of a chamber?
4)
(a) A 22.0 kg child is riding a playground merry-go-round that is rotating at 40.0 rev/min. What
centripetal force must she exert to stay on if she is 1.25 m from its center? (b) What centripetal force
does she need to stay on an amusement park merry-go-round that rotates at 3.00 rev/min if she is 8.00 m
from its center?
5)
Calculate the centripetal force on the end of a 100 m (radius) wind turbine blade that is rotating at
0.5 rev/s. Assume the mass is 4 kg.
6) A roller coaster travels in a circular loop of radius 5.0 m. At the bottom of the loop the roller
coaster car is traveling 25.00 m/s. At the top of the loop the roller coaster car is traveling 20.17
m /s .
7)
ORBITAL MECHANICS: GRAVITY AND CENTRIPETAL MOTION COMBINED
G = 6.673 x 10-11(N•m2)/kg2
Body’s Radius
Body’s Mass
Hoth’s Radius: 9.00 x 107 m Hoth’s Mass: ?
Orbit: 2.20 x 1012 m
Moon #1’s Radius: 1.74 x 106 m
Moon #1’s Mass: 2.35 x 1022 kg
Orbit: 1.08 x 108 m
Moon #2’s Radius: 3.33 x 104 m
Moon #2’s Mass: 8.05 x 1020 kg
Orbit: 8.91 x 108 m
Hoth’s Sun’s Radius: 1.55 x 107 m Mass: 1.01 x 1031 kg
1.
Some intrepid scientists from the “Rebel Alliance” sent a 100.0 kg probe to Hoth. The probe landed
on the surface of Hoth. On Hoth the probe had a WEIGHT of 595.627 N. What’s the mass of Hoth?
(Answer: 7.23 x 1026 kg )
2.
How fast is Hoth traveling around it’s sun?
3.
How many Earth years does it take for Hoth to travel around it’s sun once?
4.
How fast is Hoth’s moon #1 traveling around Hoth?
5.
What is the period of motion for Hoth’s moon #1
6.
Hoth has 6 moons. Unfortunately, due its distance from our observatories, it is difficult to measure
all the statics of the other moons. One observatory measured the speed of Hoth’s moon #3 to be
4.50 x 104 m/s. How much time does it take for this moon to travel around Hoth?
7. Not Related to the above: At one time an infamous computer company had an idea to put its own
satellite in a low orbit about 25 km above the Earth’s Surface. How fast would these satellites
travel?
8. The space shuttle travels at 17,000 mph, 7,589.288 m/s while in orbit. How far away from the
SURFACE OF THE EARTH is the shuttle?
RATIOS
Step 1: Write down a given variables in the problem
Step 2: Select a given equation has all of the variables
Step 3: Rid Fractions
Step 4: Substitute given values into the equation
Step 5: Balance problem algebraically
Example: FC: The velocity doubles and the period remains constant, The mass remains unchanged.
 𝐹𝑐 , 𝑣, 𝑇, 𝑚
2𝜋𝑣
2𝜋𝑚𝑣
 𝐹𝑐 = 𝑚𝑎𝑐 = 𝑚 ( 𝑇 ) = 𝑇




𝐹𝑐 𝑇 = 2𝜋𝑚𝑣
(_______𝐹𝑐 )𝑇 = 2𝜋𝑚(𝟐𝒗)
(__𝟐_____𝐹𝑐 )𝑇 = 2𝜋𝑚(𝟐𝒗)
Final Answer 𝑭𝒄 ⇒ 𝟐𝑭𝒄 𝒐𝒓 𝑭𝒄𝒇 = 𝟐𝑭𝒄𝒊
Centripetal
1. vt: The radius is doubled and the period is tripled
2. r: The acceleration changes by 1/4 and the period changes by a factor of 5/6
3. r: aC triples, v remains constant
4. T: v changes by a factor of 3/8, R changes by a factor of 5/2
5.
Fc: The radius triples, the velocity remains constant. The mass remains unchanged.
Gravitational
1. If the initial force at some distance, r, is 1.00 x 102 N, then what is the force of attraction at a
distance of exactly 3r ? ____________________________________________________________________________
2. If the initial force at some distance, r, is 1.00 x 102 N, then what is the force of attraction at a
distance of exactly 4r ? ____________________________________________________________________________
3. If the initial force at some distance, r, is 1.00 x 102 N, then what is the force of attraction at a
distance of exactly 1/10 r ? ________________________________________________________________________