2.1.3 Study- Conservation of Energy

A stationary ball has _______________ kinetic energy. A swiftly moving foot has ________________kinetic energy.

• a lot of, no

• no, a lot of

Tags

NGSS.MS-PS3-1

NGSS.MS-PS3-5

When a moving foot collides with a stationary ball, kinetic energy transfers ...

• from the foot to the ball

• from the ball to the foot

Answer explanation

Kinetic energy is transfered from one object to another during a collision. When a stationary object gains kinetic energy, it is set into motion.

Tags

NGSS.MS-PS2-1

NGSS.MS-PS3-1

NGSS.MS-PS3-5

After a collision between a moving foot and a stationary ball, the ball's kinetic energy, _______________ setting the ball into motion.

• decreases

• remains the same

• increases

Answer explanation

Kinetic energy is transferred from one object to another during a collision. When a stationary object gains kinetic energy, it is set into motion.

Tags

NGSS.MS-PS3-1

NGSS.MS-PS3-5

A skydiver has a mass of 80 kg. When she is at a height of 900 m, her GPE is 705,600 J. She is falling at a velocity of 32 m/s downward. What is her ME at this point?

• 664,640 J

• 746,560 J

• 40,960 J

Answer explanation

First, find the skydiver's kinetic energy:

KE = ½mv²

KE = ½(80)(32²)

KE = 40,960 J

Then add her KE to her GPE to get her ME:

ME = KE + GPE

ME = 40,960 J + 705,600 J

ME = 746,560 J

Tags

NGSS.MS-PS3-1

NGSS.MS-PS3-2

NGSS.MS-PS3-5

A second skydiver is still in the airplane, waiting to jump. He accidentally drops his helmet out the door of the plane. Complete the sentence to describe how the energy of the helmet changes as it falls to Earth.

As the helmet falls, its velocity will increase, so its KE will ______________.

• increase

• decrease

Answer explanation

As velocity increases, KE increases.

Tags

NGSS.MS-PS3-1

NGSS.MS-PS3-5

A second skydiver is still in the airplane, waiting to jump. He accidentally drops his helmet out the door of the plane. Complete the sentence to describe how the energy of the helmet changes as it falls to Earth.

As the height of the helmet decreases, its GPE will ______________.

• increase

• decrease

Answer explanation

As height decreases, GPE decreases.

Tags

NGSS.MS-PS3-2

A second skydiver is still in the airplane, waiting to jump. He accidentally drops his helmet out the door of the plane. Complete the sentence to describe how the energy of the helmet changes as it falls to Earth.

Right before it hits the ground, the helmet will have the maximum amount of ________ and the minimum amount of _______.

• GPE, KE

• KE, GPE

Answer explanation

As velocity increases, KE increases. Right before hitting Earth, the velocity and KE of the helmet will both be at their maximum.

As height decreases, GPE decreases. Right before hitting Earth, the helmet's height and GPE will both be close to zero.

Tags

NGSS.MS-PS3-2

NGSS.MS-PS3-5

What is the mechanical energy of a pendulum if it has 10 J of KE and 10 J of PE part of the way through its swing?

• Zero when it has both potential energy (PE) and kinetic energy (KE)

• The sum of its potential energy (PE) and kinetic energy (KE)

• The difference between its potential energy (PE) and kinetic energy (KE)

• Zero when either its potential energy (PE) or kinetic energy (KE) is zero

Answer explanation

The equation for mechanical energy is ME = KE + PE.

Tags

NGSS.MS-PS3-5

Which equation describes how total energy (E_total) and mechanical energy (ME) are related for this pendulum?

• E_total = ME − PE

• E_total = ME + KE + PE

• E_total = ME

• E_total = ME − KE

Answer explanation

For the pendulum in this simulation, the total energy (E_total) is equal to the mechanical energy (ME).

Which set of labels matches the systems in the diagram from left to right?

• isolated, closed, open

• open, isolated, closed

• closed, isolated, open

• open, closed, isolated

Answer explanation

In an open system, both energy and matter can leave or enter. In a closed system, only energy can leave or enter. In an isolated system, neither energy nor matter can leave or enter.

Tags

NGSS.MS-LS2-3

NGSS.MS-PS3-5