Question

A stone is thrown vertically upward with a speed of
40 m/s. The time interval for which particle was
above 40 m from the ground is (g = 10 m/s)
(1) 412 s
(2) 8s
(3) 45
(4) 2/25​

Answer 1

s=ut + (1/2×at^2)

40=40t+(1/2×10t^2)

8=8t+t^2

t^2+8t-8=0

t=...(ans)