Work and Power
Kinetic & Potential Energy
Momentum and Impulse
Transformation of Energy
Collisions
100
Two people push identical boxes across the floor for equal distances. Person A pushed the box across the room in less time than Person B. Which person had more Power? and Why?
Person A because Power is equal to Work divided by time. Since they push the same box the same distance, their work is the same. So the person with the smaller time will have a larger power.
100
What is the potential energy of a 100kg boulder sitting on a 10m tall hill?
9800J
100
What is the momentum of a 7kg ball going 8m/s?
(7)(8)=56 kgm/s
100
A ball rolls up a hill and comes to a stop at the top. What kind of transformation of energy has taken place? From ______ to _______
From kinetic energy to potential energy due to gravity
100
Which type of collision has two objects hit into each other and then stick together?
Inelastic
200
Gretta pushes a box with three times the force over twice the distance compared to Carl. How much more work does Gretta do than Carl?
W=Fd W=(3)(2) W=6 times as much force
200
What are the variables that affect how much Gravitational Potential Energy an object will have?
Mass and Height
200
What is the difference between a momentum of 10 kgm/s and -10 kgm/s
They are going in opposite directions (direction)
200
The total amount of energy in a closed, isolated system...
remains constant. Conservation of Energy
200
the total momentum of a bird and a balloon before they collide is 1000 kgm/s. What will the total momentum of the two after the collision be?
According to conservation of momentum: P after = P before so total momentum after = 1000 kgm/s
300
What is the work done to lift a 100kg box up 4 meters?
W=(100kg)(9.8)(4) W= 3920J
300
What are the variables that determine how much Kinetic Energy an object will have?
mass and velocity
300
Two identical cars are going the same speed when they hit a wall. If car A has a much larger impact time than car B, which one experiences a larger impact force?
As impact time increases, impact force decreases, so Car B will have a larger impact force than car A
300
A Ball being held over the railing of a parking deck has a potential energy of 100J. Some time after the ball is dropped, it has a potential energy of 35J. How much kinetic energy will it have at this point?.
KE1 + PE1 = KE2 +PE2 0 + 100 = KE2 + 35 100 - 35 = KE2 KE2= 65J
300
What is the only way for an object to gain or lose momentum? In other words, how do you cause a change in momentum?
an Impulse causes a change in momentum
400
What do we call the rate at which work is done?
The rate at which work is done = Power
400
If an object has a constant speed, will it have kinetic energy?
Yes, it will be KE=1/2mv^2
400
If the impact time of a collision gets 4 times longer, by what factor will the impact force change?
impact time gets bigger, impact force gets smaller. so 1/4
400
In order for energy to enter or leave a system, what has to be done?
Work
400
A ball has an initial momentum of 10 kgm/s when it hits a child who is at rest. After the collision, the ball has a final momentum of 2kgm/s. What is the final momentum of the child?
Total momentum before = total momentum after P ball before + P child before = P ball after + P child after 10 + 0 = 2 + P child after Pchild after = 8 kgm/s
500
Jessica and Dimitri run up the same flight of stairs. Jessica weighs half as much as Dimitri. Dimitri takes twice as long to get up the stairs. Which person has more Power and why?
They both have the same power. Because Jessica's force is half of Dimitri's. But he takes twice as long, and since for Power time is in the denominator, it will cause a change of 1/2 as well.
500
By what factor would the kinetic energy of a ball increase if it's velocity were tripled?
it would go up by a factor of 9 since the velocity is directly proportional and squared
500
What is the impact time needed to make a 100kg ball go from 20m/s to a stop with an impact force of 10N?
Ft=mv (10)t=(100)(20) 10t=2000 t=200 sec
500
A ball is thrown straight up, what kind of energy will it have at the top of its path?
Only potential energy. (velocity at the top of a projectile's arc is 0)
500
A car with a mass of 700kg is going 3m/s when it hits a 4kg box that is at rest. After the collision, the box bounces off with a velocity of 2m/s. What is the final velocity of the car?
total momentum before = total momentum after P car before + P box before = P car after + Pbox after (700)(3) + (4)(0) = (700)V + (4)(2) 2100 = 700V + 8 2092 = 700V V= 2.99 m/s
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