Question

n object is dropped from a height of 80 m. It will
remain in air for time [Take g = 10 m/s 2]

(1) 4 s
(2) 8 s
(3) 10 s
(4) 12 s

Answer 1

It is given that the object is dropped from height h = 80 m. Hence its initial velocity will be zero.
Also given that,
g = 10 m/s²
We have to calculate the time "t" for which the object remains in air.
t = ?
Here we use the Second equation of Motion:
s = Vi . t + 1/2 a . t²  ........ (1)
Here, s = h = 80 m/s
a = g = 10 m/s²
Putting the values, we get:
80 = (0) (t) + 1/2 (10) (t)²
80 = 5 t²
t² = 16
t = √16
t = 4 s
Hence, the object will remain in air for 4 seconds.
So, option (1) is correct.