The minimum speed with which a rock should be thrown upwards so that it rises to a height of 300 m has to be determined.
Assume that air resistance is negligible. If the rock has an initial speed of v m/s, the kinetic energy of the rock is (1/2)*m*v^2. At the highest point the rock is at 300 m. The kinetic energy of the rock here is 0 and the potential energy is m*g*h = m*9.8*300
Total energy is conserved in a closed system, which is the case here. This gives: (1/2)*m*v^2 = m*9.8*300
=> v^2 = 9.8*600
=> v = `sqrt 5880`
=> v = `14*sqrt 30`
=> v `~~` 76.68 m/s
The rock has to be thrown upwards with a minimum speed of 76.68 m/s if it has to reach a height of 300 m