40. A stone released with zero velocity from the top of a tower, reaches the ground in 4sec. The height of the tower is ( g = 10 m/s2 )

40. A stone released with zero velocity from the top of a tower, reaches the ground in 4sec. The height of the tower is ( g = 10 \(m/s^2\) )

(a) 20 m

(b) 40 m

(c) 80 m

(d) 160 m

Answer :  (c) 80 m

\( s = ut + \)\(\frac{1}{2}\)\(at^2 \)

\( = 0 + \)\(\frac{1}{2}\)\((10)(4)^2 \)

= 80 m