Study kinetic and potential energy in detail, and calculate energy transformations in real situations.
Kinetic energy is the energy of motion: KE=½mv². Potential energy is stored energy due to position: PE=mgh.
Find the kinetic energy of a 2kg object moving at 3 m/s.
KE=½×2×3²=9 J
Find the potential energy of a 5kg object raised 4m high (g=10 m/s²).
PE=5×10×4=200 J
Find the kinetic energy of a 3kg object moving at 4 m/s.
KE=½×3×16=24 J
As an object falls, its potential energy converts to kinetic energy. The total mechanical energy (KE+PE) remains constant if no energy is lost to friction.
A ball at the top of a hill has only potential energy. What happens to this energy as it rolls down?
The potential energy gradually converts into kinetic energy as the ball speeds up
Why doesn't a pendulum swing forever in real life?
Some mechanical energy is lost to friction and air resistance, converting to heat, so the total mechanical energy gradually decreases
A pendulum at its highest point has maximum potential energy and zero kinetic energy. What happens at the lowest point of its swing?
The potential energy is at its minimum (often taken as zero) and kinetic energy is at its maximum, since the pendulum moves fastest there
1. Find the kinetic energy of a 4kg object moving at 5 m/s.
2. Find the potential energy of a 2kg object raised 10m (g=10 m/s²).
3. What happens to potential energy as an object falls?
4. Write the formula for kinetic energy.
5. Write the formula for potential energy.
6. Find the kinetic energy of a 6kg object moving at 4 m/s.
7. Find the potential energy of a 3kg object raised 6m (g=10 m/s²).
8. A ball rolls down a hill. What energy transformation is occurring?
9. Write the formula for kinetic energy.
10. Why does a roller coaster need to be highest at the very start of the ride?