Can you explain what thermal energy is?

If you touch a hot light bulb and get burned, that is an example of a. radiation b. convection c. conduction

When you drop a pebble from height a it reaches the ground with speed v if there is no air resistance. from what height should you drop it so it will reach the ground with three times the speed? (a) 9m (b) 3m (c) 6m (d) 18m

What is a good example of instantaneous speed