0.1 Gravity and mechanical energy  (Page 2/5)

Gravitational potential energy

1. Describe the relationship between an object's gravitational potential energy and its:
   1. mass and
   2. height above a reference point.
2. A boy, of mass $30\mathrm{kg}$ , climbs onto the roof of a garage. The roof is $\mathrm{2,5}\mathrm{m}$ from the ground. He now jumps off the roof and lands on the ground.
   1. How much potential energy has the boy gained by climbing on the roof?
   2. The boy now jumps down. What is the potential energy of the boy when he is $1m$ from the ground?
   3. What is the potential energy of the boy when he lands on the ground?
3. A hiker walks up a mountain, $800\mathrm{m}$ above sea level, to spend the night at the top in the first overnight hut. The second day he walks to the second overnight hut, $500\mathrm{m}$ above sea level. The third day he returns to his starting point, $200\mathrm{m}$ above sea level.
   1. What is the potential energy of the hiker at the first hut (relative to sea level)?
   2. How much potential energy has the hiker lost during the second day?
   3. How much potential energy did the hiker have when he started his journey (relative to sea level)?
   4. How much potential energy did the hiker have at the end of his journey?

Kinetic energy

Kinetic Energy

Kinetic energy is the energy an object has due to its motion.

Kinetic energy is the energy an object has because of its motion. This means that any moving object has kinetic energy. The faster it moves, the more kinetic energy it has. Kinetic energy ( $E_K$ ) is therefore dependent on the velocity of the object. The mass of the object also plays a role. A truck of $\mathrm{2\; 000}\mathrm{kg}$ , moving at $100\mathrm{km}·\mathrm{hr}{}^{-1}$ , will have more kinetic energy than a car of $500\mathrm{kg}$ , also moving at $100\mathrm{km}·\mathrm{hr}{}^{-1}$ . Kinetic energy is defined as:

Consider the $1\mathrm{kg}$ suitcase on the cupboard that was discussed earlier. When the suitcase falls, it will gain velocity (fall faster), until it reaches the ground with a maximum velocity. The suitcase will not have any kinetic energy when it is on top of the cupboard because it is not moving. Once it starts to fall it will gain kinetic energy, because it gains velocity. Its kinetic energy will increase until it is a maximum when the suitcase reaches the ground.