Work, Energy, and Power
How much work must be done to stop a 1000kg car traveling at 30.6 m/s?
(-) 468,180J
Do 100 J of work in 50 s and your power output is
2.0 W
If you are driving 50 mph, will it take you twice as much distance to stop when you are driving 25 mph?
4 times the distance
A bow is drawn so that it has 40 J of potential energy. When fired, the arrow will ideally have a kinetic energy of
40 J
How much work nis done if a force of 20.0 n is exerted on an object as it moves 6.0 meters? How much power is used if it takes 3.0 seconds?
40 watts
A hammerhead with a mass of 2.0kg is allowed to fall onto a nail from a height of 0.40m. What is the maximum amount of work it could do on the nail? Why do people not just let it fall, but add their own force to the hammer as it falls?
8J
When a rifle with a longer barrel is fired, the force of expanding gases acts on the bullet for a longer distance. What effect does this have on the velocity of the emerging bullet? (Do you see why long-range cannons have such long barrels?)
Force acts for more distance, more work, more kinetic energy, more velocity. Velocity will increase
Two lumps of clay with equal and opposite momenta have a head-on collision and come to rest. Momentum is conserved, but kinetic energy seems to disappear? Where does the kinetic energy go?
It turns into heat
When the velocity of an object is doubled, by what factor is its momentum changed? Its kinetic energy?
Momentum is increased by 2. Kinetic Energy increases by 4
Why do you get lower gas mileage traveling at 50 mph than you at 75 mph?
More work, more energy, more fuel. Maintain a fast speed. More work, less time. But more gas to do 75 mph. You will eventually slow down because of friction.
Someone wanting to sell you a "Superball" claims that it will bounce to a height greater than the height from which it was dropped. Can this be? Explain.
No, because you don't have enough energy.
A projectile is fired at an upward angle of 45 degrees from the top of a 265 m tall cliff with a speed of 185 m/s. What will its speed be when it strikes the ground below. You may ignore friction.
V2 = 199M/S
Suppose that you and two classmates are discussing the design of a roller coaster. One classmate says that each summit must be lower than the previous one. Your other classmate says this is nonsense, for as long as the first one is the highest, it doesn't matter what height the others are. Whose side are you on?
both are right because you are given a certain amount of energy
Two identical arrows, one with twice the velocity of the other, are fired into a hay bale. The faster arrow will penetrate
four times as far as the slower arrow
A 0.50 kg ball is launched straight up in the air with a speed of 30.0m/s. How high with the ball go before reaching its highest height?
h2 = 45m
When a car is braked to a stop, its kinetic energy is transformed to
heat
In a gaseous mixture of massive molecules and light molecules with the same temperature (the same average KE), can type of molecule will have the greater speed?
light molecules
An object that has potential energy may have this energy because of its
location
An object that has kinetic enegy must be
moving
A job is done slowly, while an identical jod is done quickly. Both jobs require the same amount of work, but different amounts of
power
Two identical arrows, one with twice the kinetic energy of the other, are fired into a hay bale. The faster arrow will penetrate
twice as far as the slower arrow
When an object is raised above ground it gains a certain amount of potential energy. If the same object is raised twice as high it gains
twice as much potential energy
If you push an object just as far while applying twice the force you do
twice as much work
If you push an object twice as far while applying the same force you do
twice as much work
When th mass of a moving object is doubled with no change in speed, by what factor is its momentum changed? Its kinetic energy?
The momentum increases by 2. The kinetic energy increases by 2.