Work, Energy, Power

Which of the following objects has the most kinetic energy?

• A 20 kg toddler running at 5 m/s
• A 50 kg toddler running at  30 m/s
• A 90 kg toddler running at 30 m/s
• A 100 kg  toddler running at 2 m/s

Answer explanation

K = 1/2 * m * v^2

You drop a 5 kg ball from a height of 2 m. Just before it reaches the ground, what type of energy does it have?

• Potential Energy
• Kinetic Energy
• Nuclear Energy
• Chemical Energy

Answer explanation

none of the height, all of the speed --> no potential, all kinetic energy

The unit for energy and work is

• J

• N

• m/s

• m/s/s

The law of conservation states that

• every action has an equal and opposite reaction
• all matter has thermal energy
• energy cannot be created or destroyed, only changes form
• heat moves from an object of higher temperature to an object of lower temperature

The ability to do work is called

• energy
• thermal
• kinetic
• potential

A ball begins at rest at point A and is released. Which position has the most kinetic energy?

• A
• G
• D
• B

Answer explanation

ball initially had potential energy --> at lowest point, all potential transforms into kinetic

A ball begins at rest at point A and is released. Which position has the most potential energy?

• A
• G
• C
• D

Answer explanation

Gravitational Potential Energy = mgh

Therefore, greatest height --> greatest gravitational potential energy

A pendulum is released from point C.  Which statement is correct as it  swings from C to A?

• The PE increases and KE decreases
• The KE increases and PE decreases.
• The PE is maximum at A.
• The KE is maximum at C and B.

Which of the following is an example of a transformation of potential energy to kinetic energy?

• a truck slowing down
• a car climbing up a hill
• an airplane traveling at constant speed
• falling object

Mr. B's and Mr. P's classes competed in a game of tug of war. Mr. B's class pulled to the right with a force of 4,000 N. Mr. P's class pulled to the left with a force of 5,000 N. As a result the rope moved 5.1 m to the left. How much work was done by the net force?

• 4100 J
• 3100 J
• 5100 J
• 8100 J

Answer explanation

W = Fdcos(theta)

Here, F = Net force (1000 N)

d = 5.1 m

cos(0) = 1