energy changes in a system

Question 1

What is the equation for kinetic energy? Give SI units for all quantities involved.

Answer 1

½ m v²
½ x Mass x (Velocity)²
Energy (J), Mass(kg), Velocity(m/s)

Question 2

What is the equation for elastic potential energy? Give SI units for all quantities involved.

Answer 2

½ k x²
½ x Spring Constant x (Extension)²
Energy (J), Spring Constant (N/m), Extension(m)

Question 3

What is the equation for gravity potential energy? Give SI units for all quantities involved.

Answer 3

mgh
Mass x Gravitational Field Strength x Height
Energy (J), Mass(kg), Gravitational Field Strength (N/kg), Height (m)

Question 4

What is the definition of ‘Power’?

Answer 4

The rate at which energy is transferred (or rate at which work is done).

Question 5

State two equations for power. Give SI units for all quantities involved.

Answer 5

power = energy transferred/time power = work done/time
Energy (J), Work Done (J), Time (s)

Question 6

What is the unit of power?

Answer 6

Watt (W)

Question 7

Two motors lift the same mass through the same height. Motor A does this in half the time of Motor B. Which dissipates the most power?

Answer 7

Motor A.
The energy transferred is the same but the time taken is less (P=E/t).