Midterm 2 Flashcards
In rotational motion, θ is positive when measured [ ] from the positive x-axis.
counterclockwise (CCW)
In rotational motion, θ is negative when measured [ ] from the positive x-axis.
clockwise (CW)
In rotational motion, which unit represents arc length?
The arc length, s, is the distance that the particle has traveled along its circular path.
Define angular velocity (omega, w)
Angular velocity is the angular displacement through which the particle moves each second
1 mi = ? m
1 mi = 1609 m
In rotational motion, how is 1 revolution measured?
2pi
Torque (τ) is the rotational equivalent of
force.
Torque is in units of
newton-meters, N × m.
[ ] is the line starting at the pivot and extending through the point where force is applied.
Radial Line
A torque causes an angular
acceleration.
The moment of inertia is the rotational equivalent of
mass.
What is Newton’s second law of rotation?
If more than one torque acts on a rigid body about a fixed axis, then the sum of the torques equals the moment of inertia times the angular acceleration
Two conditions for static equilibrium on an extended object:
- The net force on the object must be zero.
- The net torque on the object must be zero.
A car is turning a corner at a constant speed, following a segment of a circle.
What force provides the necessary centripetal acceleration?
A. Gravity
B. Normal Force
C. Static Friction
D. Kinetic Friction
C. Static Friction
A ball at the end of a string is being swung in a horizontal circle. What force is producing the centripetal acceleration of the ball?
Gravity
Air resistance
Normal force
Tension in the string
Tension in the string
A ball at the end of a string is being swung in a horizontal circle.
What is the direction of the net force on the ball?
Tangent to the circle
Toward the center of the circle
Away from the center of the circle
There is no net force
Toward the center of the circle
Astronauts on the International Space Station are weightless because
There’s no gravity in outer space.
The net force on them is zero.
The centrifugal force balances the gravitational force.
g is very small, although not zero.
They are in free fall.
They are in free fall.
A passenger on a carnival ride rides in a car that spins in a horizontal circle as shown below.
At the instant shown, which arrow gives the direction of the net force on one of the riders?
A.
B.
C.
D.
D
If an object is rotating clockwise, this corresponds to a ______ angular velocity.
Positive
Negative
Negative
The fan blade is slowing down. What are the signs of ω and α?
ω is positive and α is positive.
ω is positive and α is negative.
ω is negative and α is positive.
ω is negative and α is negative.
ω is positive and α is zero.
ω is negative and α is positive.
The fan blade is speeding up. What are the signs of w and α?
ω is positive and α is positive.
ω is positive and α is negative.
ω is negative and α is positive.
ω is negative and α is negative.
ω is positive and α is zero.
ω is negative and α is negative
The four forces shown have the same strength. Which force would be most effective in opening the door?
Force F1
Force F2
Force F3
Force F4
Force F1
A net torque applied to an object causes
A linear acceleration of the object.
The object to rotate at a constant rate.
The angular velocity of the object to change.
The moment of inertia of the object to change.
The angular velocity of the object to change.
Two coins rotate on a turntable. Coin B is twice as far from the axis as coin A.
The angular velocity of A is twice that of B
The angular velocity of A equals that of B
The angular velocity of A is half that of B
The angular velocity of A equals that of B
Two coins rotate on a turntable. Coin B is twice as far from the axis as coin A.
Which coin has the larger linear (tangential) velocity?
A
B
They have the same linear velocity
B
Two spheres have the same radius and equal masses. One is made of solid aluminum and the other is made of a hollow shell of gold.
Which sphere has the bigger moment of inertia about an axis through its center?
Solid Aluminum Sphere
Hollow Gold Sphere
They have the same moment of inertia
Hollow Gold Sphere
An object is in equilibrium if
Fnet = 0
τnet = 0
Either A or B
Both A and B
Both A and B
The scale is positioned half-way between the mass and the pivot point. What does the scale read?
500 N
1000 N
2000 N
4000 N
2000 N
An object will be stable if
Its center of gravity is below its highest point.
Its center of gravity lies over its base of support.
Its center of gravity lies outside its base of support.
The height of its center of gravity is less than 1/2 its total height.
Its center of gravity lies over its base of support.
The restoring force of three springs is measured as they are stretched. Which spring has the largest spring constant?
A
B
C
A
A very rigid material—one that stretches or compresses only slightly under large forces—has a large value of
Tensile strength.
Elastic limit.
Density.
Young’s modulus.
Young’s modulus.
A person stands on a very light rigid board that rests on a bathroom scale at each end. The left scale reads 35 lbs and the right scale reads 105 lbs. What is the weight of the person?
70 lbs
105 lbs
140 lbs
185 lbs
140 lbs
A light plastic cart and a heavy steel cart are both pushed with the same force for 1.0 s, starting from rest. After the force is removed, the momentum of the light plastic cart is ________ that of the heavy steel cart.
Greater than
Equal to
Less than
Equal to
A 10 kg cart moves to the left with a velocity of 2 m/s, hits a wall and then moves back toward the right with a velocity of 1 m/s. What is the change of momentum Δp that the cart experiences?
–20 kg m/s
–10 kg m/s
0 kg m/s
10 kg m/s
30 kg m/s
30 kg m/s
Consider a dish falling to the ground.
What can you say about the change in momentum when it falls on a carpet verses a hard floor?
The change in momentum is less on the carpet
The change in momentum is more on the carpet
The change in momentum is the same for both carpet and floor
The change in momentum is the same for both carpet and floor
The 1-kg box is sliding along a frictionless surface. It collides with and sticks to the 2-kg box. Afterward, the speed of the two boxes is
0 m/s
1 m/s
2 m/s
3 m/s
1 m/s
The two boxes are sliding along a frictionless surface. They collide and stick together. Afterward, the velocity of the two boxes is
2 m/s to the left
1 m/s to the left
0 m/s, at rest
1 m/s to the right
2 m/s to the right
0 m/s, at rest
The two boxes are on a frictionless surface. They were sitting together at rest, but an explosion between them has just pushed them apart. The 1 kg box moves to the left at 4 m/s.
How fast is the 2-kg box going?
1 m/s
2 m/s
4 m/s
8 m/s
2 m/s
A mosquito and a truck have a head-on collision. Splat! Which has a larger change of momentum?
The mosquito
The truck
They have the same change of momentum.
They have the same change of momentum.
You awake in the night to find that your living room is on fire. Your one chance to save yourself is to throw something that will hit the back of your bedroom door and close it, giving you a few seconds to escape out the window. You happen to have both a sticky ball of clay and a super-bouncy Superball next to your bed, both the same size and same mass. You’ve only time to throw one. Which will it be?
Throw the Superball.
Throw the ball of clay.
It doesn’t matter. Throw either.
Throw the Superball.
An object’s angular momentum is proportional to its
Mass.
Moment of inertia.
Kinetic energy.
Linear momentum.
Moment of inertia.
A child is on a playground swing, motionless at the highest point of his arc. What energy transformation takes place as he swings back down to the lowest point of his motion?
K ⇒ Ug
Ug ⇒ K
Eth ⇒ K
Ug ⇒ Eth
K ⇒ Eth
Ug ⇒ K
Both skiers push off with a Force of 500 N. Which skier will be faster at the bottom of the hill?
Red Skier
Blue Skier
They will have the same speed
Blue Skier
A tow rope pulls a skier up the slope at constant speed. What energy transfer (or transfers) is/are taking place?
W ⇒ Ug
W ⇒ K
W ⇒ Eth
Both A and B.
Both A and C.
Both A and C.
Starting from rest, two identical marbles each roll down a frictionless hill both of which are at the same height. One hill is more steep than the other as shown below. Which marble is going faster at the bottom?
The marble going down the steeper hill is faster.
The marble going down the less steep hill is faster.
Both marbles have the same speed at the bottom.
Both marbles have the same speed at the bottom.
c A hockey puck sliding on smooth ice at 4 m/s comes to a 1-m-high hill. Will it make it to the top of the hill?
Yes.
No.
No.
Three balls are thrown from a cliff with the same speed but at different angles. Which ball has the greatest speed just before it hits the ground?
Ball A.
Ball B.
Ball C.
All balls have the same speed.
All balls have the same speed.
Four students run up the stairs in the time shown. Which student has the largest power output?
A.
B.
C.
D.
B.
Each of the 1.0 kg boxes starts at rest and is then pulled for 2.0 m across a level, frictionless floor by a rope with the noted force and angle. Which box has the highest final speed?
B.
If you raise an object to a greater height, you are increasing
Kinetic energy.
Heat.
Potential energy.
Chemical energy.
Thermal energy.
Potential energy.
If you hold a heavy weight over your head, the work you do
Is greater than zero.
Is equal to zero.
Is less than zero.
Is converted into chemical energy.
Is converted into potential energy.
Is equal to zero.
Which of the following is an energy transfer?
Kinetic energy
Work
Potential energy
Chemical energy
Thermal energy
Work
A person throws a javelin into the air. As she propels it forward from rest, she does 270 J of work on it. At its highest point, its gravitational potential energy has increased by 70 J. What is the javelin’s kinetic energy at this point?
270 J
340 J
200 J
–200 J
–340 J
200 J
The following pairs of temperatures represent the temperatures of hot and cold reservoirs for heat engines. Which heat engine has the highest possible efficiency?
300°C, 30°C
250°C, 30°C
200°C, 20°C
100°C, 10°C
90°C, 0°C
300°C, 30°C
The efficiency of this heat engine is
1.00
0.60
0.50
0.40
0.20
0.40
A large –20°C ice cube is dropped into a super-insulated container holding a small amount of 5°C water, then the container is sealed. Ten minutes later, the temperature of the ice (and any water that has melted from the ice) will be warmer than –20°C. This is a consequence of
The first law of thermodynamics.
The second law of thermodynamics.
The third law of thermodynamics.
Both the first and the second laws.
The second law of thermodynamics.
When you walk at a constant speed on level ground, what energy transformation is taking place?
Echem → Ug
Ug → Eth
Echem → K
Echem → Eth
K → Eth
Echem → Eth
A machine uses 1000 J of electric energy to raise a heavy mass, increasing its potential energy by 300 J.
What is the efficiency of this process?
100%
85%
70%
35%
30%
30%
Define isolated system
An isolated system is a system with no net external force acting on it, leaving the momentum unchanged.
