Work and Energy

Question 1

What is the equation for work?

Answer 1

• Work (J) = Force (N) × Distance (m)

- W = Fd

Question 2

What is the equation for gravitational potential energy?

Answer 2

Gravitational potential energy = Mass (kg) × Height (m) × gravitational Field Strength (N/kg)

Question 3

What is the equation for change gravitational potential energy?

Answer 3

• Change in gravitational potential energy = Mass (kg) × Change in Height (m) × gravitational Field Strength (N/kg)
• △Ep = m × g × △h

Question 4

What is the equation for kinetic energy?

Answer 4

• Kinetic Energy = Mass (kg) × Velocity² (m/s) × ½

- KE = ½mv²

Question 5

What is the equation for Hooke’s law?

Answer 5

• Force (N) = spring constant (N/m) × extension (m)
• F=kx
  Spring constant (stiffness) = Gradient of a force- extension graph (F/x)
  Extension = stretched length - original length

Question 6

What is the work done in stretching equation?

Answer 6

• Work done in stretching = area under a force- extension graph
• W = ½Fx (force × extension × ½)
  or
  W = ½kx² (½ x spring constant x extension²)

Question 7

Why is there always some energy lost when energy is transferred or transformed?

Answer 7

Energy is always lost to heat (friction) whenever it changes state or is transferred.

Question 8

What are the 4 main ways vehicles lose energy and what are the easy ways to improve each?

Answer 8

• Aerodynamic losses: making the car more streamline to move through the air easier.
• Rolling resistance: correctly inflates tyres and use materials that don’t heat up as easily.
• Idling losses: add stop-start systems that turns off the engine when stopped in traffic
• Inertial losses: Using lighter materials such as carbon fibre instead of heavy metal

Question 9

What are the 5 main car safety features?

Answer 9

• Seat belts
• Crumple Zones
• Air bags
• Side-impact bars
• Passenger cell

Question 10

What is the general purpose of car safety features?

Answer 10

• Increase the time of the impact and the distance the energy is transferred over to reduce the deacceleration (a = △v/t) and therefore reduce the resultant force (F=ma)
• Simply to slow the car down and the passengers over a longer period of time to reduce the force on the passengers.

Question 11

What is springs constant?

Answer 11

Springs constant is the stiffness of an elastic object

(N/m) Force per unit of measurement

Question 12

What is it meant when an object is elastic?

Answer 12

It returns to its original shape after being stretched
Or an impossible object that converts all its elastic potential energy into kinetic energy when upstretched- not to friction.

Question 13

What are the factors that affect thinking distance?

Answer 13

• Illness
• Tiredness
• Drugs
• Alcohol

Question 14

What are the factors that affect braking distance?

Answer 14

• Road surface (Weather)
• Brakes
• Mass of car
• Velocity (greatly)