phys 7
About 40 J is required to push a crate 4 m across a floor. If the push is in the same direction as the motion of the crate, the force on the crate is about
10 N.
What will the kinetic energy of a pile driver ram be if it starts from rest and undergoes a 10 kJ decrease in potential energy?
10 kJ
If you push a crate horizontally with 100 N across a 10-m factory floor and the friction between the crate and the floor is a steady 70 N, how much kinetic energy does the crate gain?
300 J
A miracle car with a 100% efficient engine burns fuel having a 40-megajoules-per-liter energy content. If air drag and overall frictional forces at highway speeds totals 1000 N, what distance per liter can be achieved on the highway?
40 km
A car's engine is 20% efficient. When cruising, the car encounters an average retarding force of 1000 N. If the energy content of fuel is 40 megajoules per liter, how many kilometers per liter does the car achieve?
8
Acrobat Bart at the circus drops vertically onto the end of a see-saw, with his partner Art equidistant from the fulcrum at the other end. Art is propelled straight upward a distance twice that of Bart's dropping distance. Neglecting inefficiencies we see
Art has half the mass of Bart.
Which requires more work: lifting a 50-kg sack a vertical distance of 2 m or lifting a 25-kg sack a vertical distance of 4 m?
Both take the same 1000 J.
An apple hanging from a limb has potential energy because of its height. If it falls, what becomes of this energy just before it hits the ground? When it hits the ground?
Immediately before hitting the ground the apple's energy is kinetic energy; when it hits the ground, its energy becomes thermal energy.
Compared with a car moving at some original speed, how much work must the brakes of a car supply to stop a car that is moving twice as fast? How will the stopping distances compare?
It takes four times the work and four times the stopping distance.
A car is raised a certain distance in a service-station lift, thus giving it potential energy relative to the floor. If it were raised twice as high, how much more potential energy would it have?
It would have twice as much potential energy.
What is recycled energy?
Reused energy that otherwise would be wasted
What is the source of energy in sunshine?
Thermonuclear fusion energy
When is the potential energy of something significant?
When the potential energy changes
How much work is done on a satellite in a circular orbit about Earth?
Zero
Rank PE from greatest to least at each point:
a, b=d, c
A block of ice sliding down an incline has half its maximum kinetic energy
at the bottom.
A ball is released from rest at the left of the metal track shown here. Assume it has only enough friction to roll, but not to lessen its speed.Rank momentum from greatest to least at each point.
c, b=d, a
Rank KE from greatest to least at each point:
c, b=d, a
Energy cannot be _______
destroyed.
Solar power is commonly used to produce
electricity.
Two identical arrows, one with twice the speed of the other, are fired into a bale of hay. Compared with penetration of the slow arrow, the faster arrow penetrates
four times as far.
The work that is done when twice the load is lifted twice the distance is _______.
four times as much.
Two identical golf carts move at different speeds. The faster cart has twice the speed and therefore has
four times the kinetic energy.
When you lift twice the load twice as high, in half the time, the increase in potential energy is _______.
four times.
A circus diver drops from a high pole into water far below. When he is halfway down
he has gained an amount of kinetic energy equal to half his initial potential energy. his potential energy is halved. his kinetic energy and potential energy are equal.
When Joshua brakes his speeding bicycle to a stop, kinetic energy is transformed to
heat.
What is the unit of work?
joule
If a Ping-Pong ball and a golf ball both move in the same direction with the same amount of kinetic energy, the speed of the Ping-Pong ball must be
more than the golf ball.
A light aluminum ball and a heavy lead ball of the same size roll down an incline. When they are halfway down the incline, they will have identical
none of the above
A bicycle that travels four as fast as another when braking to a stop will skid
sixteen times as far.
A ball rolling down an incline has its maximum kinetic energy at
the bottom.
No work is done by gravity on a bowling ball that rolls along a bowling alley because
the force on the ball is at right angles to the ball's motion.
After rolling halfway down an incline, a marble's kinetic energy is
the same as its potential energy.
If you do work on a skateboard loaded with friends in one-third the usual time, you expend
three times the usual power.
Strictly speaking, more fuel is consumed by your car if the air conditioner, headlights, or even a radio is turned on. This statement is
true.
A 1000-kg car and a 2000-kg car are hoisted to the same height. Raising the more massive car require
twice as much work.
The work you do when pushing a shopping cart a given distance while applying twice as much force is
twice as much.
A force sets an object in motion. When the force is multiplied by the time of its application, we call the quantity impulse, and an impulse changes the momentum of that object. What do we call the quantity force multiplied by distance?
work
