Work, energy and momentum

Question 1

What is ‘work done’?

Answer 1

Any force that is applied to make an object move, energy is transferred and work is done. Work done is equal to the energy transferred.

Work done (J) = Force (N) x Distance (m)

Question 2

When brake pads are applied what happens

Answer 2

Work is done to overcome the friction. The brake pad against the wheel opposes the energy of the car and so the kinetic energy of the car is transferred to the surroundings and brake pads/wheel discs

Question 3

What is the equation for the change in gravitational potential

Answer 3

Change in gravitational potential (J) = mass (kg) x Grav field strength (N/kg) x height (m)
Ep = m x g x h

Question 4

What is power

Answer 4

The rate of energy transfer

Power (W) = Energy (J) / Time (s)

Question 5

What is momentum

Answer 5

Calculated in kg m/s

All moving objects have momentum.

Question 6

What is the conservation of momentum

Answer 6

Provided no external forces act upon it, the momentum before the interaction equals the momentum after. Depending upon the opposite forces, the objects move away together or apart

Question 7

In an explosion, what happens

Answer 7

There must be a positive and a negative so the overall momentum is 0. Both have equal but opposite momentum

Question 8

What is the impact time

Answer 8

Say you run into a car at speed the force is large as the impact time is short, but if you increase the impact time, so change the momentum (slow down) the impact time increases and the force is smaller

Question 9

Name 2 ways a modern car is designed to protect you from a collision

Answer 9

Crumple zones increase the impact time, so decrease the force

Seat belts and air bags change the momentum slowly over a larger area so the force decreases