The Kinetic Energy of Objects

Question 1

What is the physics definition of work done?

Answer 1

When a force moves an object through a distance, energy is transferred and work is done.

Question 2

What is the formula for work done?

Answer 2

W = F x d

W = Work done (J)

F = force (N)

d = distance (m)

Question 3

What is gravitational potential energy?

Answer 3

The energy an object has because of its vertical position in a gravitational field. When an object is lifted, work is done against gravity and the object gains gravitational potential energy.

Question 4

What is the formula for gravitational potential energy?

Answer 4

Ep = m x g x h

Ep = Gravitational potential energy (J)

m = Mass (kg)

g = Gravitational field strength (N/kg)

h = Height (m)

Question 5

What is kinetic energy?

Answer 5

Energy possessed by anything that moves.

Question 6

What is the formula for kinetic energy?

Answer 6

Ek = 1/2 x m x v2

Ek = Kinetic energy (J)

m = Mass (kg)

v = Speed (m/s)

Question 7

What is the relation between kinetic energy and work done by brakes?

Answer 7

Kinetic energy transferred = work done by brakes

Question 8

What energy transfer occurs when a car brakes?

Answer 8

The kinetic energy in the wheels is transferred to thermal energy in the brakes.

Question 9

What energy transfer occurs when an object falls?

Answer 9

The object’s gravitational potential energy is converted into kinetic energy.

Question 10

What is the relationship between energy lost and gained when an object falls?

Answer 10

Gravitational potential energy lost = kinetic energy gained

Question 11

What is power?

Answer 11

The rate at which work is done.

Question 12

What is the formula for power?

Answer 12

P = E/t

P = Power (W)

E = Work done (J)

t = Time (secs)

Question 13

What is one watt equivalent to?

Answer 13

One joule if energy transferred per second.

Question 14

What is momentum?

Answer 14

The tendency for an object to move in the same direction.

Question 15

What is the formula for momentum?

Answer 15

p = m x v

p = Momentum (kg m/s)

m = Mass (kg)

v = Velocity (m/s)

Question 16

What is the law of conservation of momentum?

Answer 16

In a closed system, the total momentum before an event is the same after the event.

Question 17

What are regenerative brakes?

Answer 17

Brakes used in electric or hybrid cars that convert the kinetic energy of the wheels back into electrical energy.

Question 18

How do regenerative brakes work?

Answer 18

The brakes put the vehicle’s motor in reverse which causes the wheels to slow. The motor then acts as an electric generator which converts kinetic energy into electric energy which is stored as chemical energy in the vehicle’s battery.

Question 19

What are four ways that a car can be adapted to reduce the impact of car crashes in its pass angers?

Answer 19

• Crumple zones on the front and back of the car crumple on impact which increases impact time and decreases the force produced.
• Side impact bars help direct the kinetic energy of the crash away from the passengers.
• Seat belts stop the wearer from crashing into hard surfaces. They also increase the time taken for the wearer to stop which reduces the forces acting on them.
• Air bags increase stopping time and prevent passengers hitting hard surfaces.