Energy 2

Energy 2

• Is affected by speed and mass

  ex more mass and more speed = greater kinetic energy

• Object must have motion

• The kinetic energy of an object increases as its velocity increases

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Kinetic energy

Example: Juan is running on the beach with his dad. Juan has a mass of 40 kg and is running at a velocity of 2 m/s.

How much kinetic energy does he have?

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Kinetic Energy Formula

​1/2 x mass x velocity² remember ² = SQUARED

1/2 x 40 x 2²

20 x 4 = 80 JOULES

​KINETIC ENERGY IS MEASURED IN JOULES

Multiple Choice

A plane with a mass of 6,800 kg is moving at a speed of 55.0 m/s. What is the kinetic energy of the plane? $$KE\ =\frac{1}{2}mv^2$$

• 20,600,000 J.

• 10,285,000 J.

• 374,000 J.

• 187,000 J.

Multiple Choice

What is the kinetic energy of a 0.500 kg toy car moving at a speed of 1.50 m/s? $$KE\ =\frac{1}{2}mv^2$$

• 1.13 J.

• 2.25 J.

• 0.563 J.

• 0.167 J.

Multiple Choice

What is the kinetic energy of a 4.0 kg cart that is moving at a speed of 0.50 m/s? $$KE\ =\frac{1}{2}mv^2$$

• 0.50 J

• 4.0 J.

• 8.0 J.

• 2.0 J.

Multiple Choice

A scientist conducts a test to determine how best to increase the kinetic energy of a moving ball. Which change would add the most energy?

• Doubling the speed of the ball.

• Tripling the mass of the ball.

• Tripling the speed of the ball.

• Doubling the mass of the ball.

Multiple Choice

Which action will decrease the kinetic energy of a train?

• Adding more cars to the train.

• Decreasing the temperature of the train.

• Adding passengers to the train.

• Decreasing the speed of the train.

Multiple Choice

Which object has the greatest kinetic energy?

• A 2,000 kg plane moving at 30 m/s.

• A 40,000 kg boat moving at 0.1 m/s.

• A 4,200 kg truck moving at 2.0 m/s.

• A 0.01 kg paintball moving at 50 m/s.

Multiple Choice

When a book falls from a shelf, its kinetic energy _______ because its velocity _______.

• decreases; increases

• increases; increases

• decreases; decreases

• increases; decreases

Multiple Choice

The kinetic energy of an object increases as its _______ increases.

• potential energy

• gravitational energy

• height

• velocity

Multiple Select

Which variables affect the kinetic energy of an object?

• speed

• acceleration

• volume

• mass

- is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors.

Ex- A spring would have potential energy if it is sitting on a shelf, is compressed, or is stretched

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Potential Energy

when an object is closer to the ground

Decreases

when an object is higher off the ground

Increases

Potential Energy

​For example, a rock in a tree has more potential energy than a rock on the ground.

For example: A 0.145kg baseball is flying at a height of 2.50 m. How much potential energy does the ball have?

PE = mgh

PE= 0.145 x 9.81 x 2.50

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How to find potential energy

​Gravity can be inputted as 9.81

This is the gravitational acceleration on Earth

So, PE = 9.81mh

Multiple Select

A metal block is let go from a certain height. What information is needed to calculate the velocity of the metal block just before it hits the ground?

• The volume of the block.

• The temperature of the block.

• The original height of the block.

• The gravitational constant.

Multiple Choice

What is the approximate potential energy of a rock weighing 10 KG that sits on a hill 300 m high? $$PE=\ mgh;\ where\ g\ =\ 9.81;\ PE\ =\ 9.81mh$$

• 3,000 J.

• 30,000 J.

• 300 J.

• 30 J.

Multiple Choice

Which spring has more potential energy stored? $$PE=\ mgh;\ where\ g\ =\ 9.81;\ PE\ =\ 9.81mh$$

• A 1.0 N/m constant spring stretched 0.3 m.

• A 1.0 N/m constant spring stretched 0.2 m.

• A 2.0 N/m constant spring stretched 0.3 m.

• A 2.0 N/m constant spring stretched 0.2 m.

Velocity

Maximum velocity is reached at higher points

(Remember velocity is like speed but with directionality)

​ the rate of change of the object's position with respect to a frame of reference and time. It might sound complicated, but velocity is basically speeding in a specific direction.

When an object has potential energy, that means that due to its position, it can gain kinetic energy

For example, ball rolls up a hill. As the ball rolls, its kinetic energy DECREASES and its potential energy INCREASES.

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Potential and Kinetic Energy

V = √2gh gravitational constant is 9.81

V = √2(9.81)h 9.81 x 2 is 19.62

V = √19.62h Since you know velocity, you must get height alone
1. Multiply velocity by itself (V²)- this is the inverse of the square root.

2. Divide the velocity by 19.62

Ex A rocket flies directly upward with an initial velocity of 24.0 m/s. Assuming there is no air friction, what is the maximum height the rocket will reach?

24 = √19.62h 24² = √19.62h 576 = 19.62h 576/19.62 = 29.4 m

Solving for height

V = √2gh gravitational constant is 9.81

V = √2(9.81)h 9.81 x 2 is 19.62

V = √19.62h multiply 19.62 x height then square root

Example- An object is let go from a height of 1.4m, what will its velocity be?

V = √19.62 x 1.4 V = 5.2 m/s

Solving for velocity

Calculating

PE=KE (short cut)

​Full explanation: https://youtu.be/SrqPNXLNCoI

Multiple Choice

A scientist shoots a rocket straight up into the air. Which action would increase the maximum height that the rocket can reach?

• Decreasing the mass of the rocket.

• Decreasing the velocity of the rocket.

• Increasing the velocity of the rocket.

• Increasing the mass of the rocket.

Multiple Choice

A roller coaster car starts rolling down a hill from a height of 60 m. The track becomes straight at a height of 30 m. Which statement is true of the roller coaster car at 30 m?

• It has potential energy but no kinetic energy.

• It has neither kinetic energy nor potential energy.

• It has kinetic energy but no potential energy.

• It has both kinetic energy and potential energy.

Multiple Choice

A ball is thrown straight up with an initial velocity of 4.40 m/s. Assuming there is no air friction, what is the maximum height the ball will reach? $$V\ =\sqrt[]{19.62h}$$

• 0.449 m.

• 0.225 m.

• 1.98 m.

• 0.988 m.

Multiple Choice

A wooden block is let go from a height of 5.80 m. What is the velocity of the block just before it hits the ground? $$V\ =\sqrt[]{19.62h}$$

• 10.7 m/s.

• 56.8 m/s.

• 7.54 m/s.

• 28.4 m/s.