Energy and Momentum
A woman can lift barrels a vertical distance of 1 m or can roll them up a 2 m ramp to the same elevation. If she uses the ramp, the applied force required is * .
1/2
A person on a roof throws one ball downward and an identical ball upward at the same speed. The ball thrown downward hits the grand with 100 J of Kinetic energy. ignoring air friction, with how much kinetic energy does the second ball hit?
100 J
About how efficient is a typical gasoline-buring car engine
30%
An arrow in a bow has 70 J of potential energy. Assuming no loss of energy due to heat, how much kinetic energy will it have after it has been shot.
70 J
Which of the following has the largest momentum?
A pickup truck traveling down the highway
Energy is changed from one form to another with no net loss or gain
Always True
A pulley system can * .
Both change and multiply
Which has greater kinetic energy, a car traving at 30 km/h or a half-as-massive car traveling at 60 km/h
The 60 km/h
Which has more momentum, a large truck moving at 30 mph or a small truck moving at 30 mph
The large truck
If you lift one load up two stories, how much work do you do compared to lifting one load up one story?
Twice as much momentum
When you jump of a step, you usually bend your knees as you reach the ground. By doing this, the time of the im[act is about 10 times more then it would be stiff-legged. The average force on your body is reduced by * .
about 10 times
A collision is considered elastic if * .
all of the above
If the momentum of an object changes and its mass remains constant, *
all of the above
In order to increase the final momentum of a golf ball, we could * .
all of the above
A car traveling along the highway needs a certian amount of force on it to stop. more stopping force may be required when the cat has * .
all of these
A karate expert executes a swift blow and severs a cement black with her bare hand
all of these
As a pendulum swings back and forth *
all of these (at the lowest part of the swing, its energy is all kinetic, potential energy is transformed to kinetic, kinetic energy is transformed to potential)
The force of an apple hitting the ground depends upon * .
all the these
Which requires more work: lifting a 50 kg sack vertically 2 m or lifting a 25 kg sack vertically 4 m.
both are the same
A cannon recoils from launching a cannonball. The speed of the cannon's recoil is small because the * .
cannon has far more mass that the cannonball
Cannonballs are launched from an airplane in the forward direction of motion. The momentum of the airplane will be * .
decrease
A freight train rolls along a track with considerable momentum. If it were to roll at the same speed but had twice the mass, it momentum would be * .
doubled
The ratio of useful work output to total work input is called the *
efficiency
An object at rest may have * .
energy
The force that accelerates a rocket into outer space is exerted on the rocket by * .
exhaust gases
A pulley system can only change direction; it can't multiply forces as well.
false
If the net external force acting on a system is zero, then the total momentum of the system is zero.
false
Impulses are normally smaller when bouncing takes place
false
In physics, the amount of work done on an object is the product of force and time
false
Momentum is a scalar quantity
false
More power is needed to carry a heavy suitcase slowly up a fight of stairs than to carry the suitcase quickly up the same flight of stairs.
false
The rate at which work is done is called energy
false
The ratio of output to input force for a simple machine is its efficiency
false
The ratio of useful work output to total work input is mechanical advantage
false
In Physics, work is defined as * .
force times distance
How much farther will a car travel at 100 km/s skid than the same car traveling at 50 km/s?
four times
If Nellie Newton pushes an object with twice the force of twice the distance, she does * the work.
four times
While roller blading, Granny collides with her tiny grandson Ambrose who is at rest. Ignoring any friction effects, Ambrose's speed after the collision will be greatest when * .
he and Granny make a bouncing collision, each going separate ways
A cannon fires a cannonball. The speed of the cannonball will be the same as the speed of the recoiling cannon * .
if the mass of the cannonball equals the mass of the cannon
A cannonball shot from a long barrel cannon travels faster than one shot from a short barreled because the ball receives a greater * .
impulse
The momentum change of a object is equal to the * .
impulse acting on it
The reason padded dashboards are used in cars is that they *
increase the time of impact in a collision
The unit of work is the *
joule
A ball thrown in the air with 100 J of kinetic energy, which is transformed to gravitational potential energy at the top of the trajectory. When it returns to tis original level after encountering air resistance, its kinetic energy is * .
less than 100 J
Potential Energy is the energy an object has because of its * .
location
The momentum of an object is defined as the objects * .
mass times its velocity
The ratio of output to input force of a simple machine is called the * .
mechanical advantage
A heavy object and a light object are released from rest at the same height and time in a vacuum. As they fall, they have equal * .
momenta
An object that has kinetic energy must have *
momentum
If the velocity of a moving object doubles, then what else doubles
momentum
Two objects, A and B, have the same size and shape, but A is twice as heavy as B. When they are dropped simultaneously from a tower, they reach the ground at the same time, but A has a higher
momentum
A golf ball moving forward with 1 unit of momentum strikes and bounces backward off a heavy bowling ball that is initially at rest and free to move. The bowling ball is set in motion with the momentum of * .
more than 1
An object that has kinetic energy must be *
moving
An object that has linear kinetic energy must be * .
moving
If an object has kinetic energy, then it also must have * .
none of these (acceleration, momentum, force, impulse)
A moving freight car runs into an identical car at rest on the track. The cars couple together. Compared to the velocity of the first car before the collision, the velocity of the combined cars after the collision is * .
one half as large
Kinetic energy of an object is equal to * .
one half the product of it mass times speed squared
A 1N apple falls on the ground. The apple hits the ground with an impact force of about *.
ot enough information
A job is done slowly, and identical job is done quickly. Both jobs require the same amount of work but different amounts of * .
power
Superman is at rest in space when he throws an asteroid that has more mass than he does. Which moves faster, Superman or the asteroid?
superman
Suppose an astronaut in outer space wishes to play solitary "throw, bounce, and catch" game by tossing a ball against a very massive and perfectly elastic concrete wall. If the ball is as massive as the astronaut, then * .
the astronaut will not catch any bounces
If all peopel, animals, trains, an trucks all over the world began the walk or run to the east, then * .
the earth would spin a bit slower
A Ping-Pong ball launcher is fired. Compared to the force on the ball, the force on the launcher is * .
the same
A Ping-Pong ball launcher is fired. Compared to the impulse on the ball, the force on the launcher is * .
the same
Suppose a cannon is made of a strong but very light material. Suppose also that the cannonball is more massive than the cannon itself. For such a system * .
the target would be in a safer place than the operator
In order to catch a ball, a player moves his hand backward in the direction of the balls motion. Doing this reduces the force of the impact on the player's hand principally because *
the time of impact is increased
The amount of potential energy possessed by an elevated object is equal to * .
the work done to lift it
Momentum of a system is conserved only when * .
there are no net external forces acting on the system
Suppose a girl is standing on a pond where there is no friction between her feet and the ice. in order to get off the ice, she can
throw something in the direction opposite to that in which she wants to go
Automobile dashboards that are padded lengthen the amount of time of impact in a collision
true
Energy transforms from one form to another with no net loss or gain.
true
If a net force acts on a system, The system's momentum will change.
true
Impulse is defined as the force exerted on an object times the time it lasts.
true
Momentum is defined as an object's mass times its velocity
true
Perfectly elastic collisions between large objects are uncommon in the everyday world.
true
The energy a object has by virtue of its motion is kinetic energy
true
The energy n object has by virtue of its location is it potential energy
true
The rate at which work is done is called power
true
The unit of power is the watt
true
The unit of work is called a joule
true
Using an inclined plan is an effective way to lift a heavy object that you otherwise couldn't lift.
true
When a baseball player follows through when hitting the ball, the contact time with the ball is longer
true
When two objects collide and completelt bounce apart the collision is said to be elastic
true
When two objects collide and completelt stick together, the collision in inelastic
true
When we carry objects across the room, without lifting it or setting it down, we do no physical work on it.
true
If you lift two loads up two stories, how much work do oyu do compared to lifting just one load up one story?
twice
Compared to a sports car moving at 30 mph, the same sports car moving at 60 mph has * .
twice as much momentum
The unit of power is *
watt
Power is defined as the * .
work done on an object divided by the time to do the work
All simple machines ideally work on the principle that * .
work input equals work output
Recoil is noticeable if we throw a heavy ball while standing on roller skates. If instead we go through the motion of throwing the ball but hold onto it, our net recoil velocity will be * .
zero
Two gliders having the same mass and speeds move toward each other on an air track and stick together. After the collision the velocity of the gliders is * the original.
zero
A piece of putty moving with 1 unit of momentum strikes and sticks to a heavy bowling ball that is initially at rest. After the putty sticks to the ball both are set in motion with a combined momentum that is * .
1 unit
