Conservation of Mechanical Energy

Mechanical Energy

physical science

Mechanical Energy of an ISOLATED System

• the TOTAL ENERGY never changes!!!

• in the picture, total (mechanical) energy is equal to 50,000 Joules

• KE + PE HAS TO EQUAL 50,000 Joules

• look at each point: KE + PE = 50,000 J every time!

Multiple Choice

At some point during a fall, an object has 183 J of KE and 117 J of PE. What is the mechanical energy of the system?

• 300 J
• 66 J
• 21,411 J

Multiple Choice

A skydiver jumps from a plane and is halfway through her descent. At this point in time she has:

• Kinetic Energy

• Gravitational Potential Energy

• Both Kinetic and Gravitational Potential Energy

• She has no energy

Multiple Choice

An object has 300 J of total mechanical energy and 208 J of KE. How much PE does it have?

• 508 J
• 92 J
• 0.69 J

Multiple Choice

At the top of a hill, a car is sitting still and has 2,500 J of PE. What is the mechanical energy of the system?

• 2,500 J
• there is not enough information to answer the qustion
• 0 J

Multiple Choice

A car with a total mechanical energy of 2,500 J is measured to have 575 J of PE. How much KE does the car have at the same point?

• 1,437,500 J
• 1,925 J
• 3,075 J

**disclaimer: I KNOW the apple story might not be true, but everyone has heard about it, so...

Multiple Choice

Energy stored by objects due to their position above Earth’s surface.

• potential energy

• kinetic energy

• gravitational potential energy

• mechanical energy

Multiple Choice

What is the unit of measurement for potential energy?

• Watts

• Joules

• Newtons

• Meters

Multiple Choice

I have the most potential energy if I am:

• 5 feet high

• 10 feet high

• 15 feet high

• 20 feet high

Multiple Choice

A leopard with a mass of 55.00 kg climbs 12.0 m up a tree. What is its GPE?

• 6,468 J
• 660 J
• 4.58 J
• 0.22 J

Multiple Choice

Which has more gravitational potential energy?

• A 0.25 kg apple sitting on a countertop 1 meters off the ground

• A 1000 kg car sitting the driveway on the ground.

• They have the same gravitational potential energy

Multiple Choice

Acceleration due to gravity (g) on Jupiter is 24.79 m/s². If a 5 kg box is 32 m above the surface of Jupiter, calculate the GPE of the box.

• 160 J
• 3,966.4 J
• 158.66 J
• 6.45 J

Multiple Choice

If you know an object's potential energy, what operation can you use to solve for height?

• h = mg

• h = PE / (mg)

• h = mg / (PE)

• h = PE(mg)

Multiple Choice

A golf ball has a mass of 0.046 kg. It is dropped and has 1.1 J of gravitational potential energy (gravity = 9.8 m/s²). What height was it dropped from?

• 2.4 meters

• 234 meters

• 0.41 meters

• There isn't enough information to determine the height.

Multiple Choice

What is the unit of measurement for kinetic energy?

• Watts
• Joules
• Newtons
• Meters

Multiple Choice

A bicycle and a person with a total mass of 80 kg are traveling at a velocity of 7 m/s. What is their kinetic energy?

• 156,800 J

• 1,960 J

• 0.82 J

• 7,840 J

Multiple Choice

What is the kinetic energy of a 4kg shotput thrown with a velocity of 13m/s?

• 676 J

• 3.25 J

• 17J

• 338 J

Multiple Choice

Which of the following has more kinetic energy?

• A 1000 kg car moving at 10 m/s

• A 4000 kg semi truck moving at 5 m/s

• They have the same kinetic energy

Multiple Choice

If you know an object's kinetic energy, what operation would you use to solve for velocity?

• v = KE(2m)

• v = (2KE) / m

• v = [2KE/m]^0.5

• v = [KE(2m)]^0.5

Multiple Choice

What is the velocity of a ball with a mass of 5kg that has a kinetic energy of 250 J

• 5 m/s

• 7 m/s

• 10 m/s

• 50 m/s

Summary