Run away, but we're running in circles
What would happen to the centripetal force required to keep an object going in a circle if the radius of a circle was doubled?
What is 1/2?
F(c) = mv2/r
[(1)(1)2/2]/[(1)(1)^2/1]
= 1/2
How much work is done when a force of 50 N is applied but does not move a box?
What is none?
W=FxDxcos(theta)W=(50N)(0m)(1)
W=0J
Erica Jong said, "The words carry their own momentum. A confession in motion tends to stay in motion. Newton's first law of jealousy." What is the equation for the physics term she used?
What is
mass x velocity
Why does the Moon not collide with the Earth if there is an attraction?
The moon’s inertia keeps it going forward as it is falling as a projectile. This creates an orbital path around the Earth.
Which of the objects below is accelerating?
a) Object moving at constant speed along a straight line
b) Object moving at constant speed in a circle
c) Object slowing down while moving in a straight line
d) Both b and c describe accelerating objects.
What is d?
Bonus: Explain why...
How much centripetal force is required to create an inward acceleration of 2.0 m/s2 to keep a 0.60 kg object in a circular path?
Fc=
ac=2.0 m/s2
m=0.60 kg
Fc=mac
Fc=(0.60kg)(2.0 m/s2)
Sergio pushed a box with 50 N of force forward. When it did not move he pushed the box even harder with 100 N of force but the box still did not move. When did Sergio do more work?
What is neither?
Since the box does not move, the distance =0m. W=Fxdxcos(theta)
Match the equation to the event:
a) elastic collision
b) inelastic collision
c) explosion
1)m1v1 + m2v1 = (m1+m2)V'
2) mv1 = m1v1' + m2v2'
3) m1v1 + m2v2 = m1v1' + m2v2'
What are:
a-3
b-1
c-2
v^2 = v_o^2 + 2g(∆h)
and
∆KE = ∆PE
can you show that you can get the kinematic equation from the conservation of energy?
What is:
1/2m(v^2-v_o^2) = mg∆h
v^2-v_o^2 = 2g∆h
v^2 = v_o^2 + 2g(∆h)
How does a person standing on the ground explain why you, sitting on the left side of a slippery back car seat, slide to the right when the car makes a high-speed left turn?
a) You tend to move in a straight line and thus slide with respect to the seat that is moving to the left under you.
b) There is a net outward force being exerted on you.
c) The force of motion propels you forward.
The car seat pushes you forward.
What is a?
What is the centripetal acceleration of a bike traveling a tangential speed of 8 meters per second in a circle that has a radius of 5 meters?
What is 12.8 m/s2?
ac = v2/r
v = 8 m/s
r = 5m
ac = [(8m/s)2]/(5m)
A sled is pulled by a boy with a force of 60 N at 35° from the horizontal. How much work is done if the sled moved 15 m forward?
What is 735J?
W=Fxdxcos(theta) = 60N*15m*cos(35)
OR
F=60N*cos(35) = 49N
d= 15 m
W = 49N*15m
In which of these collisions is kinetic energy conserved? (inelastic collision, totally elastic collision, both)
What is total elastic collisions?
You’re riding a toboggan down an icy run to a frozen lake, and you accelerate the 80.0-kg combination of you and the toboggan from 1.0 m/s to 2.0 m/s in 2.0 s. How much power does that require?
What is 60 Watts?
What does it mean if object 1 does 10 J of work on object 2?
a) Object 1 exerts a 10-N force on object 2 in the direction of its 1-m displacement.
b) Object 1 exerts a 1-N force on object 2 in the direction of its 10-m displacement.
c) Object 1 exerts a 10-N force on object 2 at an angle 60 degrees relative to its 2-m displacement.
d) All of the above
e) None of the above
What is d?
A record takes 1.3 s to make one complete rotation. An object on this record is 0.12 m from the center. What is its velocity?
What is v=0.58 m/s?
v=?
T=1.3s
r=0.12m
v=[2(π)(r)]/T
A 0.16 kg pool ball is shot off a 0.73 m high table and the ball hits the floor with a speed of 7.1 m/s. How fast was the ball moving when it left the pool table?
What is 5.98 m/s?
In which of these collisions is momentum conserved? (inelastic collision, totally elastic collision, both)
both
A 2200kg car traveling at 30ms collides with another 2200kg car that is at rest. The two bumpers lock and the cars move forward together. What is their final velocity?
What is V'=
m1v1 + m2v2 = (m1+m2)V'
(2200kg)(30m/s) + 0 = (4400kg)V'
V' =15 m/s to the right
When would a ball hitting a wall have a greater change in momentum: when it hits the wall and bounces back at the same speed or when it hits and sticks to the wall? Explain your answer.
What is "When it hits the wall and bounces back."
*Remember happy and sad balls?
What is the force of gravity between Earth (5.972 × 1024 kg) and Mars (6.39 × 1023 kg) when they are at their minimum distance of 5.46 x 1010 meters?
*G=6.67 x 10-11
What is 8.54 x 1016 N?
F = G [m1*m2]/r2
F = (6.67x10-11) [(5.972 x 1024kg)(6.39 x 1023kg)]/ (5.46 x 1010 meters)2
A 0.16 kg pool ball was traveling at 12 m/s while 0.78 meters off the ground. How much kinetic energy does it have when it hits the ground?
12.77J
Bonus Question:
How much did it start with?
A 95 kg pitcher at rest throws a 0.15 kg baseball 40 m/s to the right. How fast would the pitcher be going after the throw on a friction-less surface?
What is 0.063 m/s to the left?
v1(m1+m2) = m1v1' + m2v2'
0 = 95(v1') +(0.15)(40 m/s to the right)
Two objects slide over a friction-less horizontal surface. The first object, m1 = 5.1 kg, is propelled with speed v1=4.5 m/s, toward the second object, m2=2.5 kg, which is initially at rest. After the collision, both objects have velocities which are directed theta = 30 degrees on either side of the original line of motion of the first object. What are the final speeds of the two objects? Is the collision elastic or inelastic?
What is v1'= 2.6 m/s and v2'= 5.2 m/s and since K(i) = K(f), the collision is elastic?
Estimate the radial acceleration of the toe at the end of the horizontally extended leg of a ballerina doing a pirouette. *assume the ballerina's leg to be 0.80 m in length and she completes a full turn in 1s
What is about 30 m/s2?
Assume the length of ballerina’s leg to be 0.80 m. Suppose that she completes a full turn in 1 s. The speed of her toe would be V = 2πr/T = 2(π)(0.80m)/1s = 5 m/s
a = v2/r = 25/0.8 = 30 m/s2