Physics Energy and Momentum Test
Recoil is noticeable if you throw a heavy ball while standing on roller skates. If instead you go through the motions of throwing the ball but hold onto it, what would by your net recoil velocity?
it will be 0
What are the forms of mechanical energy?
kinetic and potential energy
Which type of energy is associated with a body in motion?
kinetic energy
Which has the largest momentum, a large truck at rest or a small car moving at highway speed?
the small truck
PEe formula
PEe=1/2kx^2
Which type of energy is associated with a body's height above the ground?
PEg
If the distance of stretch, x, is tripled for a particular spring, by what factor does the stored potential energy change?
9 times
When a car's speed triples, what happens to its kinetic energy?
9x as much
PEg formula
PEg=mgh
dissipated energy formula
Ediss=ffx
What are the 2 units of energy?
Joules and watts
Kinetic energy
KE=1/2mv^2
What are the units for the spring constant k?
N/M
A roller coaster car starts with an initial speed of 0.39 m/s from the top of a section of a track that is sloping down at 26° to the horizontal. After traveling 81.0 m, it reaches the end of that section of the track and continues up the next section of the track that slopes up at 22° to the horizontal. If this section of the track has a length of 72.2 m, will the car reach the top of the section? Assume that you can neglect friction and that the car has no source of power.
Since the cart has more energy than is needed to get to the top of the next hill it will make it.
Impulse Momentum Theorem
The impulse on an object is equal to the object's final momentum minus the object's initial momentum
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 will the conservation of momentum hold? Will the force on the cannonball be greater than the force on the cannon? Would it be safe to stand at the target location?
Yes it still holds, the forces would be the same, it would be safe because the cannon would have a larger acceleration than the canon ball.
What conditions for force and time will result in the smallest change in momentum?
a small force and short period of time
If two balls of identical size are dropped from a tower, but ball A has a mass of 10kg and ball B has a mass of 20 kg when the reach the ground at the same time, which ball will have the larger acceleration? Which ball will have the larger speed? Which ball will have the larger momentum?
acceleration and speeds will be the same, the 20kg ball will have a larger momentum
A skier travels down a slope toward the bottom of the hill. At what point(s) on the slope will gravitational potential energy and kinetic energy be equal? Ignore the effects of friction.
at the halfway point
Must an object that has kinetic energy be falling? Must it be moving? Can it be at rest? Must it be elevated?
does not need to be moving or elevated, cannot be at rest
During a collision of a baseball and bat, when will the baseball's velocity reach zero?
during the collision
A gymnast falls from a height onto a trampoline. For a moment, both the gymnast's kinetic energy and gravitational potential energy are zero. How is the gymnast's mechanical energy stored for that moment?
elastic potential energy
Which type of energy is associated with a spring?
elastic potential energy
What is the area under a Force vs displacement graph?
energy
State the Law of the Conservation of Energy
energy can't be created or destroyed in a closed system
What is Hooke's law?
f=kx
How can you determine impulse from a graph of Force (N) vs time (s) ?
find the area under the curve
What must be included in any system where there is gravitational potential energy?
height
In the collision of two billiard balls, one ball moves from east to west and impacts a second ball that is initially at rest. That second ball moves northeast to southwest, while the first ball continues on its east- west path. Is this possible? Why or why not?
impossible, momentum is not conserved in all directions
A moving freight car runs into an identical car at rest on the track. The cars couple together. How does the velocity of the combined cars after the collision compare to the velocity of the first car before the collision?
it is a 1/2 less
If the mass of a particle were to suddenly drop to zero, what would happen to the momentum of the particle?
momentum will be 0
force formula given mass time and velocity
mv=ft
In an elastic collision do the object stick together?
no
In an elastic collision to the objects get warmer?
no
In an elastic collision, is there lasting deformation of the objects?
no
Suppose an astronaut in outer space wishes to toss a ball against a very massive and perfectly elastic concrete wall and catch it as it bounces back. If the ball is as massive as the astronaut, will the astronaut be able to catch the ball at all?
no
A 200 N box of books is carried across a 10 m room at a constant velocity. Ignoring the initial acceleration of the box, determine the work performed on the box.
no work is done because force and displacement are perpedicular
If a heavy object and a light object are released from rest at the same height and time in a vacuum. As they fall, do they have equal energies? Weights? Momenta?
no, no, no
Under what circumstances is the following statement true? "If two skaters standing still push against each other, the speed of the first is the same as the speed of the second, and in the opposite direction."
only when both masses are the same
power formula
p=w/t
A meteor that originally was heading south breaks up into two chunks. One of the chunks moves southwest. In what direction should you should look for the other chunk?
southeast
What is the slope of a force vs displacement graph for a spring?
spring constant
What can be done to increase the final momentum of a golf ball? (three things)
swinging the bat harder, increasing the time of impact, increasing the force
A piece of putty and a rubber ball have the same mass. If you drop them from the same height, which object will produce a greater impulse?
the ball
How much farther will a car traveling at 100 km/s skid than the same car traveling at 50 km/s?
the distance would be x4
A rocket leaves a launch pad at liftoff with a great deal of upward momentum. What was initially given downward momentum?
the expelled fuel
Which has greater kinetic energy, a car traveling at 30 km/h or a half-as-massive car traveling at 60 km/h?
the half as massive car
What is the momentum change of an object equal to?
the impulse acting on it
When a baseball player catches a ball, he or she moves their hand backward in the direction of the ball's motion. Why does doing this reduce the force of impact on the player's hand?
the time of impact is increased
What value is the amount of potential energy possessed by an elevated object is equal to: the power used to lift it, the distance it is lifted, the work done in lifting it, g, or the force needed to lift it.
the work done in lifting it
A snowball thrown at an ice cream truck at Valley Forge in January sticks to the side. Into what form of energy was the mechanical energy changed?
thermal energy (friction)
If a toy cannon is fired, how does the impulse on the ball compare to the impulse on the cannon?
they are equal
A small economy car (low mass) and a limousine (high mass) are pushed from rest across a parking lot, equal distances with equal forces. Which car receives more kinetic energy?
they receive the same amount of kinetic energy
If you are stuck on a pond where there is no friction between your feet and the ice, what could you do to get off the ice?
throw something the opposite direction you want to go
What is the reason padded dashboards are used in cars?
to increase the time of impact
work formula
w=fdcosθ
When is the momentum of a system conserved?
when there is no external force acting on it
If a cannon fires a cannonball, when would the speed of the cannonball be the same as the speed of the recoiling cannon?
when they have the same mass
If one job is done slowly, and an identical job is done quickly do both jobs require the same amount of work but different amounts of energy? Power?
work and energy are the same, power is not
State the Work Energy Theorem
work done= change in energy
What is Power defined as?
work/time
If the momentum of an object changes and its mass remains constant, is it accelerating (or decelerating)?
yes
If the momentum of an object changes and its mass remains constant, is its velocity changing?
yes
If the momentum of an object changes and its mass remains constant, is there a force acting on it?
yes
In an elastic collision do the object have the same shape as before the collision?
yes
Can an object at rest have energy?, speed?, velocity?, momentum?
yes, no, no
A car traveling along the highway needs a certain amount of force exerted on it to stop. Would more stopping force may be required when the car has less stopping distance? Would more stopping force may be required when the car had more momentum? Would more stopping force may be required when the car has more mass?
yes, yes, yes
