Answer:2.45 m/s
Explanation:
Given
Launch velocity
launch angle
as the vertical velocity first decreasing to zero and then increases to original value so its avg is zero .



thus 

I think the answer is Helium.
Please tell me if I'm wrong.
final velocity = 0
acceleration = - 10 m/ s 2
distance. = 20 m
u = ?
v^2 - u ^2 = 2 a s
0^2 - u^ 2 = 2 * -10 * 20
-u^2 = -400
u = √ 400
u = 20m / s
I think the anser is B ::::::::::::;:;;;;;;;;;;;;;;;;;;;;;;;;;
B. Barometer is used to measure atmospheric pressure.