Kinetic energy

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Definition of Kinetic Energy

Kinetic energy is the energy an object or system has because it is moving.
It is often called the energy of motion.
A flying bee, a racing motorcycle, flowing water, and a spinning saw blade are all moving, so they all have kinetic energy — mass and material do not matter, only motion does.
A stop street sign, two chairs, and an apple (at rest) do not have kinetic energy because they are not moving.

A flying bee, a racing motorcycle, flowing water, and a spinning saw blade

Factors Affecting Kinetic Energy

An object's kinetic energy depends on two factors: mass and speed.
The greater the mass, the more kinetic energy the object has.
The greater the speed, the greater the kinetic energy.
Kinetic energy is proportional to mass and grows with the square of speed.
A car travelling at 200 km/h has more kinetic energy than at 100 km/h.

Mass and Kinetic Energy Investigation

Rolling balls of different masses down a ramp into a paper cup shows how mass affects kinetic energy.
In the experiment, a glass marble (20.4 g) moved the cup 208 cm, a plastic marble (9.5 g) moved it 107 cm, and a styrofoam ball (0.2 g) moved it 0 cm.
The pattern: as mass increases, the distance the cup moves increases, indicating more kinetic energy.
This evidence supports that moving objects with more mass have more kinetic energy.

Marble mass vs. distance moved

Speed and Kinetic Energy Investigation

Rolling a toy car at different speeds and measuring how far it travels shows how speed affects kinetic energy.
In the experiment, a slow car moved 250 cm, a medium car moved 882 cm, and a fast car moved 1450 cm.
The pattern: as speed increases, the distance the car travels increases, indicating more kinetic energy.
This evidence supports that objects with more speed have more kinetic energy.

Toy car speed vs. distance travelled

Kinetic vs. Potential Energy

Potential energy is stored energy, such as a ball at the top of a ladder or petrol in a tank.
Kinetic energy is the energy of motion, such as a moving car or flowing water.
Some systems have both types, like a high jumper at the peak of a jump (has potential energy and some kinetic energy).
A mountain biker at the top of a mountain has potential energy; a race-car at maximum speed has kinetic energy.
A spring in a pinball machine before release has potential energy; a running refrigerator motor has kinetic energy.

A high jumper going over the bar

Energy Transfers and Conservation

The Law of Conservation of Energy states that energy cannot be created or destroyed, only transferred or transformed.
Energy transfers occur between systems, e.g., a kettle plugged in transfers electrical energy to thermal energy to heat water.
In a high jumper's jump, as she rises, kinetic energy is converted to potential energy; at the top, she has maximum potential energy and minimum kinetic energy.
When she falls, potential energy converts back to kinetic energy.

Real-World Applications

Wind is moving air particles, so they have kinetic energy.
Food contains stored potential energy that our bodies use for movement and functions.
A baseball has more kinetic energy than a wiffle ball when hit with the same force because it has more mass.
A full cart has more kinetic energy than an empty cart moving at the same speed due to greater mass.

A baseball bat about to hit a wiffle ball, and a baseball bat hitting a baseball

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1.What is kinetic energy?
Easy
- AEnergy stored in an object due to its position
- BEnergy of an object due to its motion
- CEnergy released during chemical reactions
- DEnergy transferred by heat
2.Which factor does kinetic energy depend on?
Easy
- AMass and speed
- BMass and height
- CSpeed and temperature
- DHeight and temperature
3.A car and a bicycle are moving at the same speed. Which has more kinetic energy?
Medium
- AThe car
- BThe bicycle
- CBoth have the same kinetic energy
- DIt depends on the direction of motion
4.If the speed of an object doubles, its kinetic energy becomes:
Medium
- ATwice as much
- BFour times as much
- CHalf as much
- DThe same
5.A 2 kg ball is moving at 3 m/s. What is its kinetic energy?
Hard
- A3 J
- B6 J
- C9 J
- D18 J
6.The SI unit of kinetic energy is the:
Easy
- ANewton
- BJoule
- CWatt
- DPascal
7.A moving object has kinetic energy. When it comes to a stop, the kinetic energy is:
Medium
- ADestroyed
- BConverted to other forms of energy
- CStored as potential energy
- DIncreased
8.Two objects have the same kinetic energy. Object A has twice the mass of object B. How do their speeds compare?
Hard
- ASpeed of A is half that of B
- BSpeed of A is √2 times that of B
- CSpeed of A is 1/√2 times that of B
- DSpeed of A is twice that of B

Thêm câu hỏi

9.Which of the following is an example of kinetic energy?
Easy
- AA stretched rubber band
- BA book on a shelf
- CA moving car
- DA charged battery
10.The kinetic energy of an object depends on the frame of reference. This means:
Medium
- AKinetic energy is the same for all observers
- BKinetic energy can be negative
- CDifferent observers may measure different kinetic energies for the same object
- DKinetic energy is always conserved
11.A 0.5 kg ball is thrown with a kinetic energy of 100 J. What is its speed?
Hard
- A10 m/s
- B14.1 m/s
- C20 m/s
- D200 m/s
12.Kinetic energy is a form of energy that:
Easy
- AIs stored in objects
- BIs associated with motion
- CIs released in nuclear reactions
- DIs related to temperature
13.A car of mass 1000 kg is moving at 20 m/s. A truck of mass 2000 kg is moving at 10 m/s. Which statement about their kinetic energies is correct?
Medium
- AThe car has more kinetic energy than the truck.
- BThe truck has more kinetic energy than the car.
- CBoth have the same kinetic energy.
- DThe kinetic energy of the car is twice that of the truck.
14.A ball is thrown vertically upwards with an initial kinetic energy of 100 J. Air resistance is negligible. When the ball returns to its starting point, what is its kinetic energy?
Hard
- A0 J
- B50 J
- C100 J
- D200 J
15.Which of the following is the correct formula for kinetic energy?
Easy
- AKE = mgh
- BKE = 1/2 mv²
- CKE = mv
- DKE = 1/2 mv
16.Two balls, one of mass 1 kg and one of mass 2 kg, are dropped from the same height. Ignoring air resistance, which statement about their kinetic energies just before hitting the ground is correct?
Hard
- AThe 1 kg ball has half the kinetic energy of the 2 kg ball.
- BThe 2 kg ball has half the kinetic energy of the 1 kg ball.
- CBoth balls have the same kinetic energy.
- DThe 1 kg ball has twice the kinetic energy of the 2 kg ball.
17.A cyclist is pedaling on a level road. Which energy conversion is taking place?
Medium
- AChemical energy to kinetic energy
- BKinetic energy to chemical energy
- CPotential energy to kinetic energy
- DKinetic energy to potential energy
18.A spacecraft is in a circular orbit around Earth. Which statement about its kinetic energy is correct?
Medium
- AIt increases as the spacecraft moves.
- BIt decreases as the spacecraft moves.
- CIt remains constant.
- DIt is zero because there is no gravity.
19.A ball of mass 0.2 kg is thrown with a speed of 10 m/s. What is its kinetic energy?
Hard
- A1 J
- B10 J
- C20 J
- D100 J
20.Which of the following has kinetic energy?
Easy
- AA book sitting on a shelf
- BA stretched rubber band
- CA moving car
- DA charged battery
21.A student uses a ramp to launch a toy car. She measures the speed of the car at the bottom of the ramp. She then increases the height of the ramp. What will happen to the speed of the car at the bottom?
Medium
- AIt will decrease.
- BIt will stay the same.
- CIt will increase.
- DIt will increase then decrease.
22.The kinetic energy of an object is measured to be 50 J. If its mass is 4 kg, what is its speed?
Hard
- A2.5 m/s
- B5 m/s
- C10 m/s
- D25 m/s
23.A student drops a ball from different heights onto a block of clay. She measures the depth of the dent made in the clay. Which graph shows the relationship between the drop height and the dent depth? (Assume the ball transfers all its kinetic energy to the clay.)
Medium
- AA straight line through the origin
- BA curve that gets steeper as height increases
- CA horizontal line
- DA curve that flattens out as height increases
24.In an experiment, a student releases a toy car from rest at different heights on a ramp. The car rolls down and then travels along a horizontal surface before hitting a block. The distance the block is pushed is measured. Which of the following would be the most appropriate control variable?
Hard
- AThe mass of the toy car
- BThe height of the ramp
- CThe distance the block is pushed
- DThe type of surface on the ramp
25.A student uses a ticker timer to record the motion of a trolley on a level track. The tape shows dots that get farther apart. What can be concluded about the kinetic energy of the trolley?
Medium
- AIt is increasing
- BIt is decreasing
- CIt is constant
- DIt is zero
26.A student investigates the relationship between the speed of a moving object and its kinetic energy. She uses a spring to launch a trolley of fixed mass. She compresses the spring by different amounts and measures the speed of the trolley after launch. Which of the following should she plot to test if KE is proportional to v²?
Hard
- AKE against v
- BKE against v²
- Cv against KE
- Dv² against KE
27.A ball of mass 0.2 kg is dropped from a height of 5 m. What is its kinetic energy just before it hits the ground? (Take g = 10 m/s², ignore air resistance.)
Medium
- A10 J
- B5 J
- C1 J
- D20 J
28.A student uses a ramp to launch a toy car. She measures the speed of the car at the bottom of the ramp. She then increases the height of the ramp by a factor of 4. By what factor does the speed at the bottom increase? (Assume no friction.)
Hard
- A2
- B4
- C16
- D√2
29.A student places a ball at the top of a ramp and releases it. The ball rolls down and hits a block at the bottom, pushing it a certain distance. She repeats the experiment with a ball of the same size but twice the mass, released from the same height. How does the distance the block is pushed compare?
Medium
- AIt is twice as far
- BIt is the same
- CIt is four times as far
- DIt is half as far
30.In an experiment to measure the kinetic energy of a moving trolley, a student uses a light gate connected to a timer. The trolley has a card of length 10 cm attached. The timer records a time of 0.2 s as the card passes through the light gate. What is the speed of the trolley?
Medium
- A0.5 m/s
- B2 m/s
- C50 m/s
- D0.02 m/s
31.A student investigates how the kinetic energy of a pendulum bob changes during its swing. She measures the speed of the bob at the lowest point. Which of the following correctly describes the energy changes?
Hard
- AGravitational potential energy is converted to kinetic energy as the bob swings down
- BKinetic energy is converted to gravitational potential energy as the bob swings down
- CThe total energy of the bob decreases as it swings
- DThe kinetic energy is constant throughout the swing
32.A student uses a ramp to launch a toy car. She measures the speed of the car at the bottom of the ramp. She then adds mass to the car and releases it from the same height. What happens to the speed at the bottom? (Assume no friction.)
Medium
- AIt stays the same
- BIt increases
- CIt decreases
- DIt becomes zero
33.A student drops a ball from a height of 2 m onto a force sensor. The sensor measures the force during the impact. Which of the following would increase the maximum force measured?
Hard
- ADropping the ball from a greater height
- BUsing a lighter ball of the same size
- CDropping the ball onto a softer surface
- DUsing a ball that bounces less
34.A student sets up an experiment to measure the kinetic energy of a rolling ball. She measures the mass of the ball and its speed using a light gate. Which of the following is the correct formula to calculate the kinetic energy?
Medium
- AKE = mv²
- BKE = 1/2 mv²
- CKE = 1/2 mv
- DKE = mv
35.What is the SI unit of kinetic energy?
Easy
- Ajoule
- Bnewton
- Cwatt
- Dpascal
36.A 0.5 kg ball is moving with a speed of 4 m/s. What is its kinetic energy?
Medium
- A4 J
- B2 J
- C8 J
- D1 J
37.In an experiment, a student releases a toy car from rest at different heights on a ramp. The car rolls down and then travels along a horizontal surface before hitting a block. The student measures the distance the block is pushed. Which graph shows the relationship between the release height and the distance the block is pushed?
Hard
- Aa straight line through the origin
- Ba curve that gets steeper as height increases
- Ca horizontal line
- Da curve that levels off as height increases
38.A student rolls a ball down a ramp and measures its speed at the bottom. She then repeats the experiment with a ball that has twice the mass, released from the same height. How does the kinetic energy of the heavier ball compare to that of the lighter ball at the bottom? (Assume no energy loss.)
Medium
- AIt is twice as much.
- BIt is four times as much.
- CIt is the same.
- DIt is half as much.

Ghi chú ôn tập

## Kinetic Energy - Key Points - **Kinetic energy** is the energy an object has due to its motion. - It depends on **mass** and **speed**: heavier or faster objects have more kinetic energy. - The formula is: **KE = ½ mv²** where m = mass (kg), v = speed (m/s), KE = energy in joules (J). - Kinetic energy increases with the **square of speed**: doubling speed quadruples KE. - It can be transferred between objects or transformed into other forms (e.g., heat, potential energy). - **Work** is done to change kinetic energy: work = force × distance (in direction of motion). - The same amount of work is needed to stop a moving object as was used to start it. - Examples: - A moving bicycle has kinetic energy; pedaling converts chemical energy to KE. - Coasting uphill converts KE to gravitational potential energy. - Brakes convert KE to heat via friction. - In everyday situations (speeds much less than light), the formula KE = ½mv² is accurate. ## Key Terms

Kinetic energy: The energy an object possesses due to its motion.
Joule: The SI unit of energy; one joule equals the work done by a force of one newton over a distance of one meter.
Mass: The amount of matter in an object, measured in kilograms (kg).
Speed: How fast an object is moving, measured in meters per second (m/s).
Work: The transfer of energy when a force moves an object over a distance; work = force × displacement in the direction of the force.
Potential energy: Stored energy that an object has due to its position or condition (e.g., gravitational potential energy).

Thẻ ghi nhớ

What is kinetic energy?

Kinetic energy is the energy an object has because of its motion.

What two factors does kinetic energy depend on?

Kinetic energy depends on the mass and speed of the object.

Write the formula for kinetic energy in classical mechanics.

KE = 1/2 mv², where m is mass and v is speed.

What is the SI unit of kinetic energy?

The joule (J).

What is the English unit of energy?

The foot-pound.

How does doubling the speed of an object affect its kinetic energy?

Doubling the speed quadruples the kinetic energy (since v is squared).

How does doubling the mass of an object affect its kinetic energy?

Doubling the mass doubles the kinetic energy (since mass is directly proportional).

What is the relationship between kinetic energy and work?

The kinetic energy of an object equals the work needed to accelerate it from rest to its speed.

What happens to kinetic energy when an object slows down?

The object does work equal to its kinetic energy to decelerate to rest.

Give an example of kinetic energy being transformed into another form.

A cyclist coasting up a hill converts kinetic energy into gravitational potential energy.

What does the Greek word 'kinesis' mean?

It means 'motion', and is the root of the word 'kinetic'.

Who coined the term 'kinetic energy'?

William Thomson (Lord Kelvin) around 1849–1851.

What experiment showed that penetration depth is proportional to the square of impact speed?

Willem 's Gravesande's experiment dropping weights into clay.

What is the approximation condition for the classical kinetic energy formula?

It is a good approximation only when speed is much less than the speed of light.

Can kinetic energy be negative?

No, because mass and the square of speed are always positive.

Does kinetic energy depend on the observer's frame of reference?

Yes, kinetic energy depends on the relative motion between the object and the observer.

What happens to kinetic energy in a perfectly circular orbit?

It remains constant because there is almost no friction in near-Earth space.

In an elliptical orbit, where is kinetic energy greatest?

At closest approach to the massive body (periapsis).

What is the sum of kinetic and potential energy in an isolated system?

The sum remains constant (conservation of mechanical energy).

Give an example of kinetic energy being converted to heat.

Applying brakes on a bicycle converts kinetic energy to heat via friction.

What form of energy does a cyclist use to increase kinetic energy?

Chemical energy from food.

What is the term for the energy of motion?

Kinetic energy.

What is the difference between kinetic and potential energy?

Kinetic energy is energy of motion; potential energy is stored energy due to position or configuration.

Can kinetic energy be transferred between objects?

Yes, for example in collisions.

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