Conservation of Energy

A rubber band has potential energy of 5 J. If the spring constant of the rubber band is 50 N/m, what is the displacement of the rubber band?

0.4

The compressed spring of a dart gun has potential energy of 50 J. If the spring constant is 200 N/m, what is the displacement of the spring? 0.5

0.7

mghi=

1/2mvf²

1/2mvi²+mghi=

1/2mvf²+mghf

This energy transformation diagram represents the energy of a boulder, initially positioned on top of a mountain. As it falls, its original gravitational potential energy is converted to kinetic energy and air friction. How much of the energy is kinetic?

110

A ski lift is used to transport people from the base of a hill to the top. If the lift leaves the base at a velocity of 15.5 m/s and arrives at the top with a final velocity of 0 m/s, what is the height of the hill? Round the answer to the nearest tenth.

12.3

A 100 kg roller coaster car is located at the top of a hill where the height is 20 m. What is the velocity when it reaches the bottom of the hill?

19.8

What is the potential energy of a spring that is compressed 0.65 m by a 25 kg block if the spring constant is 95 N/m?

20 j

A 200 kg roller coaster car is located at the top of a hill where the height is 30 m. What is the velocity when it reaches the bottom of the hill?

24.2

A 440 kg roller coaster car is going 26 m/s when it reaches the lowest point on the track. If the car started from rest at the top of a hill, how much higher was that point on the track than the lowest point? (Use g = 9.80 m/s2, and ignore friction.)

34

Using this energy transformation diagram of a battery powered drill, what is the drill's thermal energy output?

35 j

A famous motorcycle company has just built its first electric model. Like all vehicles, the purpose of the motorcycle is to put out kinetic energy. How much energy goes toward kinetic energy?

400 j

A 10 kg ball is released from the top of a hill. How fast is the ball going when it reaches the base of the hill? Approximate g as 10 m/s2 and round the answer to the nearest tenth.

5.5

A box is sliding along a frictionless surface and gets to a ramp. Disregarding friction, how fast should the box be going on the ground in order to slide up the ramp to a height of 2.5 meters, where it stops? (Use g = 9.8 m/s2.)

7

Disregarding air resistance, what is the speed of a ball dropped from 12 feet just before it hits the ground? (Use 1 ft = 0.30 m, and use g = 9.8 m/s2.)

8.4

Irving, a cat, has a favorite toy that is made up of a squeaky ball at the end of a string. The toy makes up a closed system. Irving's owner dangles the toy so that the ball swings down and then swings back up again. Ignoring any friction, how are kinetic and potential energy related to each other as the ball swings back and forth?

As the ball moves upward, kinetic energy decreases and potential energy increases.

A spring attached to a mass is at rest in the initial position (not shown). The spring is compressed in position A and is then released, as shown in position B. Which equation describes conservation of energy in position A?

E=1/2kx²

KEi+PEi=

KEf+PEf

Which objects have both potential and kinetic energy? Check all that apply.

NOT a boulder resting on top of a mountain a sky diver who is midway through his descent to the ground a falling raindrop NOT a parked car a roller coaster car halfway down the second hill

A box is released from rest and slides down a ramp in a closed system. Even though the box speeds up, its kinetic energy at the bottom of the ramp is less than the potential energy that it had at the top of the ramp. What best explains why the box's final kinetic energy is less than its initial potential energy?

Some potential energy was converted into thermal energy due to friction.

A 535 kg roller coaster car began at rest at the top of a 93.0 m hill. Now it is at the top of the first loop-de-loop. This roller coaster's track is nearly frictionless, so resistance can be ignored. Using g = 9.8 m/s2, what best describes the roller coaster car when it is at the top of the loop-de-loop?

The car has both potential and kinetic energy, and it is moving at 24.6 m/s.

Which statements best describe the law of conservation of energy? Check all that apply.

The total amount of energy in the universe remains constant. NOT Energy can be created or destroyed. Energy cannot be created or destroyed. Energy can change from one type to another. In a closed, isolated system, energy is conserved.

system

a group of related objects that interact and form a complex whole

closed system

all forms of matter and energy are not allowed in or allowed to leave. it is isolated and energy remains constant

open system

allows some forms of matter and energy to either go in or out

elastic potential energy (PEe=1/2 kx²)

determined by the displacement aka distance the spring is compressed x, and the compressibility of the spring aka the spring constant, k.

friction is involved when

energy is converted form one form to another

any object moving through the air

force of experiences air resistance

What term is used to describe a system that loses energy to objects that are not part of the system?

open system

In a motor, the _______ of output work to input work, expressed as a percentage, is the efficiency of the motor.

ratio

constant

staying the same; unchanging

potential energy (PEg=mgh)

stored energy that results from the position or shape of an object

kinetic energy (KE=1/2mv²)

the energy an object has due to its motion

Law of Conservation of Energy

the law that states the total amount of energy in a system must remain constant, but can change form. the total amount of energy in the universe remains constant. energy can change from one form to another.

Efficiency

the ratio of output work to input work expressed as a percentage

Frictional forces acting on an object are often converted into _____ energy, which causes the temperature of the object to rise slightly.

thermal