The distance, d, through which a stone falls from rest varies directly as the square of the time, t, taken. If the stone falls 45cm in 3 seconds, how far will it fall in 6 seconds?

Options

1. 90cm
2. 135cm
3. 180cm
4. 225cm

The correct answer is C.

Explanation:

d α t² d = t² k

where k is a constant. d = 45cm, when t = 3s; thus 45 = 3² x t

k =  = 5

thus equation connecting d and t is d = 5t² when t = 6s, d = 5 x 6²

= 5 x 36

= 180cm