Initial velocity: A person jumps and reaches a height of 0.8 m...?

Question

A person jumps and reaches a height of 0.8 m. What is their initial velocity?

I have
gravity = -9.8m/s^2
height = 0.8m
final velocity (mid air) = 0
I don't have:
time or intial velocity.

I'm not sure which equation to use?

(this is a theoretical question from a physics text)

Answer 1

you do not need time
use this:

v^2 = v0^2 +2ax

you know v = 0 (velocity at midair)
and you're trying to solve for v0 (initial velocity)
and you know a = -9.8
and you know x = 0.8
just plug and chug

v0^2 = 2*9.8*.8
v0^2 = 15.68
v0 = 3.96 m/s

Answer 2

You have to use one of the four kinematics formulas.

For constant speed:
v = l/t or d/t
For constant acceleration:
d = Vit + 1/2 at2
Vf2 = Vi2 + 2ad
Vf = Vi + at

That should get you started.

Answer 3

Vo = 2.9 m/s no longer "ms" ? = 0.70 rad = 0.70(fifty seven.3°) = 40.a million° Voy = Vo(sin 40.a million) = 2.9(sin 40.a million) = a million.87 m/s time to attain max top = t = Voy/g = a million.87/9.80 one = 0.one hundred ninety s max top = a million/2gt² = (0.5)(9.80 one)(0.1904415)² = 0.18 m ANS

Answer 4

0.8m - 9.8t^2 = 0

time = 0.2857141 seconds

velocity -19.6 t

intial velocity 5.6 meters per second

Answer 5

V(final) ^ 2 - V(initial)^2 = 2 ad

- V^2 = 2 *-9.8 * 0.8

V^2 = 15.68

V = 3.96 m/s

Answer 6

Do your own homework

Answer 7

http://hyperphysics.phy-astr.gsu.edu/hbase/traj.html

try this site. It has all the formulas and answers you need