• Support PF! Buy your school textbooks, materials and every day products Here!

Help With finding initial vertical speed

  • #1

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?/
 

Answers and Replies

  • #2
Doc Al
Mentor
44,912
1,170
What's the final velocity? (When it reaches the max height.)
 
  • #3
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/.
 
  • #4
is the finaly velocity 0?
 
  • #5
Doc Al
Mentor
44,912
1,170
is the finaly velocity 0?
Of course. :wink:
 
  • Like
Likes 1 person
  • #6
ohh ok... so would i use the same formula i used above to find the initial vertical speed?
 
  • #7
what equation should i use to calculate the initial vertical speed?
 
  • #8
Doc Al
Mentor
44,912
1,170
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.
 
  • #9
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?
 
  • #10
Doc Al
Mentor
44,912
1,170
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?
 
  • #11
you add 141.12 to the 0 and then find square root of 141.12?
 
  • #12
Doc Al
Mentor
44,912
1,170
you add 141.12 to the 0 and then find square root of 141.12?
Sure! Basic algebra.
 
  • #13
so the initial vertical speed would be 11.8793939239 m/s ?
 
  • #14
Doc Al
Mentor
44,912
1,170
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.)
 
  • Like
Likes 1 person
  • #15
ok, i have one more question i need help with....
 

Related Threads on Help With finding initial vertical speed

  • Last Post
Replies
2
Views
9K
  • Last Post
Replies
14
Views
15K
  • Last Post
Replies
7
Views
4K
Replies
1
Views
2K
  • Last Post
Replies
8
Views
1K
  • Last Post
Replies
2
Views
2K
Replies
2
Views
5K
Replies
3
Views
10K
Replies
2
Views
7K
Top