A stone is thrown straight up from the ground with an initial speed of 15.2 m/s. At the same instant, a stone is dropped from a height of h meters above ground level. The two stones strike the ground simultaneously. Find the height h. The acceleration of gravity is 9.8 m/s 2. Answer in units of m.

47 m

Explanation:

Time of flight of stone thrown up = time of fall of stone dropped down.

Time of flight = 2u / g

where u is initial velocity and g is acceleration due to gravity.

= 2 x 15.2 / 9.8

=3.10 s.

For fall of second stone

time of fall t = 3.1 s

Height h = ?

h = ut +.5 g t²

= 0 +.5 x 9.8 x 3.1 x 3.1

= 47 m