# Help With finding initial vertical speed

mithilsheth

## Homework Statement

A Ball is thrown upwards. What is its initial vertical speed? The acceleration of gravity is 9.8 m/s2 and maximum height is 7.2 m ,. Neglect air resistance.

## Homework Equations

Vfinal squared = velocity initial squared + 2g times change in y

## The Attempt at a Solution

velocity final squared = velocity initial squared + 2 (-9.8)(7.2)
VF^2= VI^2 + -141.12
what now?/

Mentor
What's the final velocity? (When it reaches the max height.)

mithilsheth
the final velocity is not given. all that is given is v0, max height is 7.2 meters, and that the acceleration of gravity is 9.8 m/s/s/.

mithilsheth
is the finaly velocity 0?

Mentor
is the finaly velocity 0?
Of course. • 1 person
mithilsheth
ohh ok... so would i use the same formula i used above to find the initial vertical speed?

mithilsheth
what equation should i use to calculate the initial vertical speed?

Mentor
ohh ok... so would i use the same formula i used above to find the initial vertical speed?
Just use that equation you started with and solve for the initial speed.

mithilsheth
how do i set it to be that velocity initial squared is on the left side of the equal sign, and velocity final squared is on on the right side?

Mentor
how do i set it to be that velocity initial squared is on the left side of the equal sign, and velocity final squared is on on the right side?
The final velocity is zero, so your equation becomes:

0 = Vi2 - 141.12

So how to get Vi2 alone? How can you get rid of that - 141.12?

mithilsheth
you add 141.12 to the 0 and then find square root of 141.12?

Mentor
you add 141.12 to the 0 and then find square root of 141.12?
Sure! Basic algebra.

mithilsheth
so the initial vertical speed would be 11.8793939239 m/s ?

Mentor
so the initial vertical speed would be 11.8793939239 m/s ?
Yes. But please round off to a reasonable number of significant figures. (2 or 3 is plenty.)

• 1 person
mithilsheth
ok, i have one more question i need help with....