Physics Midterm
What will the kinetic energy of a pile driver ram be if it starts from rest and undergoes a 10 kJ decrease in potential energy?
10 kJ
What is the acceleration of a car moving along a straight road that increases its speed from 0 to 100 km/h in 10 s?
10 km/h·s
An object is lifted vertically 2.0 m and held there. If the object weighs 90 N, how much work was done in lifting it?
180 J
What did Galileo discover about moving bodies and force in his experiments with inclined planes?
In the absence of a retarding force, a body will keep moving at a constant speed in a straight line forever.
What is inertia?
Inertia is the tendency of a body to maintain its state of motion in the absence of applied forces.
When Dr. Hewitt pulls the tablecloth, why do the items on the tablecloth do what they do?
Inertia makes them stay at rest.
What kind of speed is registered by an automobile speedometer?
Instantaneous speed
Use the "Mass of elephant" slider to set the mass of the elephant to somewhere in the middle of the range. After you have set the "Mass of elephant" slider, do not change it again for this question. How would the acceleration change if the applied force on the elephant were increased?
It increases
Consider the video demonstration that you just watched. Which of the following changes would make it more likely for the ball to hit both the white can and the green can?
None of the above
Find the energy turned into heat.
Q = 630 J
Why is it advantageous to roll with the punch in boxing?
Rolling with the punch increases contact time, which decreases the force.
Why is a force that is applied for a short time more effective in karate?
The average force is increased.
What did Galileo discover about the amount of speed a ball gained each second when rolling down an inclined plane? What did this say about the ball's acceleration?
The ball had constant acceleration, so it gained the same speed every second.
Dr. Hewitt has clay "blobs" hanging on either side of his head in this video. When he turns around, what happens to the blobs?
The blobs tend to stay where they were.
For the same force, why does a long cannon impart more speed to a cannonball than a short cannon?
The force is applied for a longer time in the long cannon.
How does the force of friction for a sliding object vary with speed?
The force of friction is approximately independent of speed.
An object cannot remain at rest unless which of the following holds?
The net force acting on it is zero.
If a block is moving to the left at a constant velocity, what can one conclude?
The net force applied to the block is zero.
What is the net force on a cart that is pulled to the right with 100 pounds of force and to the left with 30 pounds of force?
The net force is 70 pounds to the right.
What is the net force on a bag pulled down by gravity with a force of 18 newtons and pulled upward by a rope with a force of 18 newtons?
The net force is zero newtons.
A 3.0-kg object moves to the right at 4.0 m/s. It collides head-on with a 6.0-kg object moving to the left at 2.0 m/s. Which statement is correct?
The total momentum both before and after the collision is zero.
A truck weighs twice as much as a car, and is moving the speed of the car. Which statement is true about the truck's kinetic energy compared to that of the car?
The truck has 8 times the kinetic energy of the car
If the equally massive cars of the preceding question stick together after colliding inelastically, how does their speed after the collision compare with the initial speed of car A?
Their speed is half the initial speed of car A.
What is the source of energy in sunshine?
Thermonuclear fusion energy
When Dr. Hewitt pulls the tablecloth, what happens to the items on the tablecloth?
They tend to stay where they were.
Some alphabet letters are floating in a bowl of soup. You want to move a letter that is far away from you closer to you. How could you rotate the bowl to do that?
Unfortunately, neither rotating the bowl clockwise nor rotating it counterclockwise will work.
What is the main difference between speed and velocity?
Velocity includes a direction, but speed does not.
If a car moves with a constant velocity, does it also move with a constant speed?
Yes, because constant velocity requires constant speed in the same direction.
You tell your friend about the neat tablecloth trick that Dr. Hewitt demonstrated. Your friend tries to repeat this trick at home and later complains to you that it failed. Which of the following is most likely the reason that it failed?
Your friend pulled the tablecloth too slowly.
When you stand at rest on a bathroom scale, how does your weight compare with the support force from the scale?
Your weight is equal in magnitude and opposite in direction to the support force from the scale.
The slow of a velocity versus time graph gives:
acceleration
mass and weight
are two different quantities
In the absence of an external force, a moving object will:
move with constant velocity
A massive block is being pulled along a horizontal frictionless surface by a constant horizontal force. The block must be __________.
moving with a constant nonzero acceleration
If the dart's exit speed is 13.5m/s and the length of the blowgun is 1.15m , find the time the dart is in the barrel.
t = 0.170 s
A dart leaves the barrel of a blowgun at a speed v. The length of the blowgun barrel is L. Assume that the acceleration of the dart in the barrel is uniform. Find a time that the dart moves inside the barrel.
t = 2L/v
When one does twice the work in twice the time, the power expended is _______.
the same
When a cue ball strikes an 8 ball head-on in a game of pool, the cue ball _______.
transfers its momentum to the 8 ball.
What is its average velocity during this 8.0-s interval?
v = -39 m/s
If you walk 5.0 m horizontally forward at a constant velocity carrying a 10-N object, the amount of work you do is:
zero
When you sit on a chair, the resultant force on you is:
zero
A 50-N object was lifted 2.0 m vertically and is being held there. How much work is being done in holding the box in this position?
0 J
What is the acceleration of a car that maintains a constant velocity of 100 km/h for 10 s?
0 km/h·s
Convert 1.2 times 10-3 to decimal notation
0.0012
Suppose a ball of putty moving horizontally with 1 kg·m/s of momentum collides with and sticks to an identical ball of putty moving vertically with 1 kg·m/s of momentum. What is the magnitude of their combined momentum?
1.41 kg·m/s
If you are 5'10 tall, what is your height in meters? (1 in=2.54 cm)
1.8 m
Given the measurements 10 m, 10 m/s, and 10 m/s2, which is a measure of speed, which is a measure of distance, and which is a measure of acceleration?
10 m is distance, 10 m/s is speed, and 10 m/s2 is acceleration.
Car goes from 40 m/s to 80 m/s in a distance of 200 m. What is its average acceleration?
12 m/s2
How far does a horse travel if it gallops at an average speed of 25 km/h for 30 min?
12.5 km
Consider a book that weighs 15 N at rest on a flat table. How many newtons of support force does the table exert on the book?
15 newtons up
You (50-kg mass) skate on ice at 4.0 m/s to greet your friend (40-kg mass), who is standing still, with open arms. As you collide while holding each other, with what speed do you both move off together?
2.2 m/s
A person of weight 480 N stands on a scale in an elevator. What will the scale read when the elevator is accelerating downward at 4.00 m/s2?
284N
A sports car of mass 1000 kg can accelerate from rest to 27 m/s in 7.0 s. What is the average forward force on the car?
3.9 times 103 N
What is the average speed in kilometers per hour of a horse that gallops a distance of 15 km in a time of 30 min?
30 km/h
If you push a crate horizontally with 100 N across a 10-m factory floor and the friction between the crate and the floor is a steady 70 N, how much kinetic energy does the crate gain?
300 J
A 2000-kg car, traveling to the right at 30 m/s collides with a brick wall and comes to rest in 0.20 s. What is the average force the car exerts on the wall?
300,000 N to the right
A 60-kg skier starts from rest from the top of a 50-m high slope. What is the speed of the slier on reaching the bottom of the slope? (Neglect friction)
31 m/s c
Write the number 0.00045 in power of ten notation
4.5 times 10-4
A car travels at 15 m/s for 10 s. It then speeds up with a constant acceleration of 2.0 m/s2 for 15 s. At the end of this time, what is its velocity?
45 m/s
A handball of mass 0.10 kg traveling horizontally at 30 m/s, strikes a wall and rebounds at 24 m/s. What is the change in momentum of the ball?
5.4 kg m/s
An object has a mass of 60 kg on the Earth. What is the mass of the object on the surface of the Moon where the acceleration due to gravity is only 1/6 of that on the Earth?
60 kg
What must be your average speed in order to travel 350 km in 5.15 h?
68.0 hm/h
What is the momentum of a 2000-kg truck traveling at 35 m/s?
7.0 times 104 kg m/s
If you are driving 72 km/h along a straight road and you look to the side for 4.0 s, how far do you travel during this inattentive period?
80m
An object sits on a frictionless surface. A 16-N force is applied to the object, and it accelerates at 2.0 m/s2. What is the mass of the object?
: 8.0 kg
Compared to yesterday, you did 3 times the work in one-third the time. To do so, your power output must have been:
: 9 times yesterday's power output
Which undergoes the greatest change in momentum (if all of the baseballs have the same speed just before being caught and just after being thrown)?
A baseball that is caught and then thrown back
Which requires more work: lifting a 50-kg sack a vertical distance of 2 m or lifting a 25-kg sack a vertical distance of 4 m?
Both take the same 1000 J.
What two units of measurement are necessary for describing speed?
Distance and time
Joanne drives her car with a mass of 1000 kg at a speed of 16m/s . Find a road friction force that is need to bring her car to a halt in 11s .
F = 1500 N
If you stand next to a wall on a frictionless skateboard and push the wall with a force of 40N , how hard does the wall push on you?
F = 40 N
A car carrying a 76-kg test dummy crashes into a wall at 30m/s and is brought to rest in 0.10 s. Find the average force exerted by the seat belt on the dummy.
F = −2.3×10^4 N
Which of the following is an accurate statement?
If an object is acted on by a non-zero net external force, its momentum will not remain constant.
Distinguish between force and impulse.
Impulse is force times a time interval.
What type of path does a moving object follow in the absence of a force?
It continues to move in a straight line at a constant speed.
A block of mass 2kg is acted upon by two forces: 3N (directed to the left) and 4N (directed to the right). What can you say about the block's motion?
It could be moving to the left, moving to the right, or be instantaneously at rest.
Use the "Force applied" slider to set the force applied on the elephant to somewhere in the middle of the range. After you have set the "Force applied" slider, do not change it again for this question. How would the acceleration change if the mass of the elephant were increased?
It decreases
What is the distance fallen for a freely falling object 1 s after being dropped from a rest position? What is the distance for a 4-s drop?
It falls 5 m in 1 s and 80 m in 4 s.
What is the gain in speed per second for a freely falling object?
It gains approximately 10 m/s.
When the speed of a moving car is doubled, how much more kinetic energy does it have?
It has four times as much.
When an object is thrown upward, how much speed does it lose each second (ignoring air resistance)?
It loses 10 m/s of speed each second until it reaches the high point, then it gains 10 m/s each second.
What does it mean to say that momentum is conserved?
It means momentum does not change.
Compared with a car moving at some original speed, how much work must the brakes of a car supply to stop a car that is moving twice as fast? How will the stopping distances compare?
It takes four times the work and four times the stopping distance.
You slam on the brakes of your car in a panic, and skid a certain distance on a straight, level road. If you had been traveling twice as fast, what distance would the car have skidded, under the same conditions?
It would have skidded 4 times farther
A car is raised a certain distance in a service-station lift, thus giving it potential energy relative to the floor. If it were raised twice as high, how much more potential energy would it have?
It would have twice as much potential energy.
Impulse = change in momentum: Ft=Δmv. How much impulse stops a 50-kg carton sliding at 4.6m/s when it meets a rough surface?
J = 230 N⋅s
An acorn falls from a tree. Compare its kinetic energy K, to its potential energy U
K increases and U decreases
A ball falls from the top of a building, through the air (air friction is present), to the ground below. How does the kinetic energy (K) just before striking the ground compare to the potential energy (U) at the top of the building?
K is less than U
If the force of friction on the crate is a steady 70 N, find the KE gained by the crate.
K= 720 J
Belly-flop Bernie dives from atop a tall flagpole into a swimming pool below. His potential energy at the top is 9000J (relative to the surface of the pool). What is his kinetic energy when his potential energy reduces to 1000 J?
KE = 8000 J
A ping-pong ball moving easing at a speed of 4 m/s, collides with a stationary bowling ball. The ping-pong ball bounces back to the west, and the bowling ball moves very slowly to the east. Which object experiences the greater magnitude impulse during the collision?
Neither; both experienced the same magnitude impulse
The unit of mass is the kilogram, and the unit of weight is the _______.
Newton
How does Newton's first law of motion relate to Galileo's concept of inertia?
Newton refined Galileo's concept of inertia and made it his first law of motion.
Can work be done on a system is there is no motion?
No, because of the way work is defined
What did Copernicus say about the motion of the Sun?
The Sun is stationary and Earth circles it.
Suppose that a car traveling to the East (+x direction) begins to slow down as it approaches a traffic light. Make a statement concerning its acceleration.
The car is decelerating, and its acceleration is negative
An apple hanging from a limb has potential energy because of its height. If it falls, what becomes of this energy just before it hits the ground? When it hits the ground?
The energy is kinetic energy before it hits the ground; it is thermal energy after.
If you push on a crate with a horizontal force of 100 N and it slides at constant velocity, what is the magnitude and direction of the frictional force acting on the crate?
The frictional force on the crate is 100 N opposite the direction of motion.
Why doesn't a heavy object accelerate more than a light object when both are freely falling?
The ratio of the weight to mass is the same for all objects in the same locality.
What is the resultant of a pair of one pound forces at right angles to each other?
The resultant is a force of 1.41 pounds in a direction bisecting the 90-degree angle between the two vectors.
What is the speed acquired by a freely falling object 5 s after being dropped from a rest position? What is the speed 6 s after?
The speed is 50 m/s after 5 s and 60 m/s after 6 s.
Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How does the speed of car B compare with the initial speed of car A?
The speed of car B is equal to the initial speed of A.
Why do the alphabet letters tend to do what they do when you rotate the bowl?
They have inertia−the tendency of an object at rest to stay at rest.
Why do the clay blobs do what they do when Dr. Hewitt turns around?
They have inertia−the tendency of an object at rest to stay at rest.
One pound is the same as 4.45 newtons. What is the weight in pounds of 1 newton?
W = 0.220 lb
The second floor of a house is 6 m above the street level. How much work is required to lift a 310-kg refrigerator to the second-story level?
W = 1.8×10^4 J
How much work is done when you push a crate horizontally with 150N across a 9.0-m factory floor?
W = 1400 J
Work = force × distance: W=Fd. Calculate the work done when a 14-N force pushes a cart 3.8m.
W = 53 J
Which depends on gravity?
Weight
You throw a ball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down.
Work is - on the way up and + on the way down
Once the crate is sliding, how hard do you push to keep it moving at constant velocity?
You push with a force equal to and opposite the dynamic friction force.
If your mass is 70kg , find your acceleration.
a = 0.57 m/s^2
Acceleration: a=Fnet/m. Calculate the acceleration of a 260000-kg jumbo jet just before takeoff when the thrust on the aircraft is 170000N .
a = 0.65 m/s^2
Consider a mass of 1 kg accelerated 1 m/s2 by a force of 1 N. Find the acceleration for a force of 2 N acting on 2 kg.
a = 1 m/s^2
A car takes 11s to go from v=0m/s to v = 28m/s at constant acceleration. If you wish to find the distance traveled using the equation d=1/2at2, what value should you use for a?
a = 2.5 m/s^2
Consider a 44-kg block of cement that is pulled sideways with a net force of 240N . Find its acceleration.
a = 5.5 m/s^2
Two forces, of magnitude 4N and 10N, are applied to an object. The relative direction of the forces is unknown. The net force acting on the object __________.
cannot have a magnitude equal to 5N
How far will it fall during this time?
d = -310 m
If the net work done on an object is negative, then the object's kinetic energy:
decreases
The area under a curve in a velocity versus time graph gives"
displacement
Action- reaction forces are:
equal in magnitude but point in opposite directions
To impart the greatest momentum to an object, you must
exert the greatest force over the longest time.
Which of the Newton's laws best explains why motorists should buckle up?
first law
When you lift twice the load twice as high, in half the time, the increase in potential energy is _______.
four times
An impulse can be increased by
increasing the force or increasing the time interval.
The total mechanical energy of a system:
is constant, only if conservative forces act
A freight car moves along a frictionless level railroad track at constant speed. The car is open on top. A large load of coal is suddenly dumped into the car. What happens to the velocity of the car?
it decreases
A slowly moving ship can have a greater momentum than a fast-moving racing car when _______.
its mass times velocity is greater than that of the car.
What is the correct unit of work expressed in SI units?
kg m2/s2
An object of mass m is hanging by a string from the ceiling of an elevator. The elevator is moving upward, but slowing down. What is the tension in the string?
less than mg
When a cannon fires a cannonball, the cannon will recoil backward because the
momentum of the cannonball and cannon is conserved.
Impulse = Ft. What impulse occurs when an average force of 7.0N is exerted on a cart for 2.0s ?
p = 14 kg⋅m/s
Momentum = mv. What is the momentum of an 7.4-kg bowling ball rolling at 2.8m/s ?
p = 21 kg⋅m/s
The quantity that is called impulse can be measured by the _______.
product of force and time.
When hitting a tennis ball with your racquet, the force on the ball has the same magnitude as the force on the _______.
racquet
If you push twice on hard against a stationary brick wall, the amount of work you do
remains constant at zero
When a big fish swims into an oncoming smaller fish and swallows it, the momentum of the two-fish system _______.
remains the same.
When a cannonball is fired, the momentum of the system (cannon + cannonball) is conserved if
the momentum of the cannon is equal to the magnitude of the momentum of the cannon ball and points in the opposite direction.
What is the instantaneous velocity of a freely falling object 8.0s after it is released from a position of rest?
v = -78 m/s
You are standing in a moving bus, facing forward, and you suddenly fall forward. You can imply from this that the bus's:
velocity decreased
When two vehicles collide, momentum is conserved _______.
whether the collision is elastic or inelastic.
The area under the curve, on a Force versus position (F vs. x) graph, represents:
work
