Kinematics Question

[Arrow_Raider]

If I am given the initial height of something that is thrown downward and the velocity of the object when it hits the ground, how do I go about determining the initial velocity? (Earth's gravity is a factor in this problem - it controls acceleration).

[fartman_900]

Well, you can use energy conservation (the easiest) or this equation Vf^2 = Vi^2 + 2*g*D, where Vf is the final velocity, Vi the initial, g is gravity and D is the distance. Remeber that this only applies with a constant acceleration.

[DomoCobra]

The height is the distance(S)
the final velocity is (V)
acceleration is gravity-9.82 (A)

you want to find Initial Velocity (U)

use this equation
v^2=U^2 + 2AS

rearrange to get
sqrt(v^2-2AS)=U

and this gives you the answer so all you have to do is put in your values
A=9.81
S=your height
V=your final velocity

ps sqrt means the sqaure root of

Hope this post helps!

[zaza]

The equation:

v^2 = u^2 +2as

where v = final velocity
u = initial velocity
a = accel.
s = distance


is the same as using energy conservation.

The initial energy is kinetic + gravitational. The final energy is kinetic only.

So 1/2 m u^2 + m g s = 1/2 m v^2

Cancel the 'm' and multiply through by 2 and you have v^2 = u^2 + 2as.



zaza