Download «First_» «Last» Kinetic Energy Problems Ek = 1/2mv2 1. What is the

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Kinetic Energy Problems
Ek = 1/2mv2
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What is the kinetic energy of a 750kg car traveling at 14m/s?
How much work must be done on the car to bring it to rest?
A rifle can shoot a 4.20g bullet at a speed of 965m/s.
a. Find the kinetic energy of the bullet
b. What work is done on the bullet if it starts from rest?
A comet with a mass of 7.85x1011kg strikes the earth at 25km/s. Find the energy of the comet.
If 2.2x106 Joules of work are needed to accelerate a 5700kg trailer truck to 26m/s, how fast would
it go if only half as much work was done?
How fast would the truck go if twice as much work was done?
Potential Energy Problems
Ep = mgh
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A 90kg rock climber first climbs 45m up to the top edge of a quarry, then, from the top, descends
85m to the bottom. Find the potential energy of the climber at the edge and at the bottom, using
the initial height as a reference level.
A 50kg shell is shot from a cannon on the earth’s surface to a height of 400m.
a. What is the potential energy with respect to the earth surface at that height?
b. What is the change in potential energy if the shell falls to a height of 200m?
A person weighing 630N (m x g) climbs a ladder to a height of 5.0m,
a. How much work is done?
b. What is the increase in potential energy?
c. Where does the energy come from to do this work?
A pendulum is made from a 7.26kg bowling ball hanging on a 2.5m long rope. The ball is pulled
back until it makes an angle of 45º with the horizontal.
a. What is the potential energy of the ball?
b. What is your reference level?
Review of Energy
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Describe the work and the energy changes taking place when
a. You climb a rope
b. You throw a ball horizontally
c. A horizontally thrown ball is caught in a mitt.
d. A horizontally thrown ball falls and gains velocity vertically.
A student is doing a problem involving a ball falling down a well. If the top of the well is chosen
as a reference point for potential energy, then what is the relationship between the potential energy
at the top and at the bottom?
Describe the work done and energy changes taking place when, using a toy dart gun,
a. You push the dart into the barrel, squeezing a spring.
b. After pulling the trigger the spring expands and the dart leaves the gun.
c. The dart sticks on the wall.
In an experiment, a student uses an air hose to exert a constant horizontal force on a block on a
frictionless table. The student is told to keep the air aimed at the block during the time the block
moves a fixed distance.
a. In terms of work and energy, explain what happens.
b. The experiment is now repeated. Everything is the same except the mass of the block is
less. What results will be the same? What will be different? In what way?