Question

27. A ball is projected vertically upward from the
ground. The ball is at the same height at t = 3 S
and t = 9 s. The height of ball at t = 5 s is
(g = 10 ms-2)
(1) 180 m
(2) 175 m
(3) 135 m
(4) 200 m​

Answer 1

Answer:

ans is in the picture. hope you understand

Answer 2

answer : option (2) 175m

explanation : A ball is projected vertically upwards from the ground with speed u m/s.

then according to formula,

s = ut + 1/2 at²

here, a = -g

so, s = ut - 1/2 gt²

a/c to question,

The ball is at the same height at t = 3 S

and t = 9 s

so, s = u(3) - 1/2g(3)² = 3u - 9g/2 .....(1)

and s = u(9) - 1/2 g(9)² = 9u - 81g/2.....(2)

from equations (1) and (2),

we get, 6u - (81g - 9g)/2 = 0

⇒6u = 72g/2

⇒u = 6g .......(3)

from equation (1), s = 3(6g) - 9g/2

= 27g/2

now height of ball at t = 5s , h = u(5) - 1/2g(5)²

= 6g(5) - 25g/2 [ from equation (3)]

= 30g - 25g/2

= 35g/2

= 35 × 10/2 = 35 × 5 = 175m

hence, option (2) is correct choice.