Calculating energy changes (Ek and Ep) | Exit Quiz | Oak National Academy

The principle of (a)   states that total amount of energy at the end of a process is always the same as the total amount of energy at the beginning.

Answer explanation

During a process, energy may be transferred between different energy stores, but the total energy in the stores at the beginning is always the same as the total energy in the stores at the end.

Tags

NGSS.MS-PS3-5

A rock on a cliff has 1600 J of energy in the gravitational store. It falls off the cliff onto the ground below. During the fall, no energy is dissipated. What is the energy transfer during the fall?

• 1600 J is transferred from the kinetic to the gravitational store.

• 1600 J is transferred from the gravitational to the kinetic store.

• Less than 1600 J is transferred from the gravitational to the kinetic store.

• More than 1600 J is transferred from the gravitational to the kinetic store.

• More than 1600 J is transferred from the kinetic to the gravitational store.

Answer explanation

Since no energy is transferred to the thermal store, all of the 1600 J that is in the gravitational store at the start transfers to the kinetic store during the rock’s fall.

Tags

NGSS.MS-PS3-5

NGSS.MS-PS3-2

Answer explanation

Energy in the gravitational store at maximum height = mass × gravitational field strength × height = 0.20 × 10 × 2.1 = 4.2 J. So the energy in the kinetic store at the start is 4.2 J.

Tags

NGSS.MS-PS3-5

NGSS.MS-PS3-1

A plate is dropped. If no energy is dissipated during the fall, the final speed of the plate before it hits the ground is 4 m/s. If energy is dissipated, which of these statements is correct?

• The final speed will be less than 4 m/s.

• The final speed will be 4 m/s.

• The final speed will be more than 4 m/s.

• It is impossible to say whether the final speed will be more or less than 4 m/s.

Answer explanation

Some of the energy from the gravitational store is transferred to the thermal store, so less energy goes into the kinetic store during the fall. If the plate gains less kinetic energy, then it will gain less speed.

Tags

NGSS.MS-PS3-5

NGSS.MS-PS3-1

Answer explanation

Energy in the gravitational store at the top of hill = mass × gravitational field strength × height = 30 × 10 × 12 = 3600 J. So the energy in the kinetic store at the bottom of the hill is 3600 J.

Tags

NGSS.MS-PS3-5

NGSS.MS-PS3-2

NGSS.MS-PS3-4

Tags

NGSS.MS-PS3-5

NGSS.MS-PS3-2