What makes a scientifically sound experiment?

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

Asystematic approach to problem solving is called a (an)

The diagram shows a series of volcanic island and a hot spot determine the direction of movement of the tectonic plate that for the island