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

Conservation of energy of a baseball problem

  • Thread starter hks118
  • Start date
  • #1
19
0

Homework Statement


A baseball is thrown from the roof of a building of height 21.2m with an initial velocity of magnitude 10.7 m/s and directed at an angle of 54.4 degrees above the horizontal.

a. What is the speed of the ball just before it strikes the ground? Use energy methods and ignore air resistance.

b.What is the answer for part (A) if the initial velocity is at an angle of 54.4 below the horizontal?

Homework Equations


PE=mgh
KE=1/2mv^2

KEi+PEi=KEf+PEf

The Attempt at a Solution


I'm not exactly sure where to begin. I'm thinking I have to find the max height the ball achieves using projectile motion methods then use conservation of energy?
 

Answers and Replies

  • #2
Filip Larsen
Gold Member
1,237
169
You can find the answer using just the equations you cited. If you are puzzled, try see which of the four terms in the last equation (i.e. conservation of mechanical energy) you know and if that will let you determine the value you seek. Besides doing the actual calculation the problem is also meant to make you think about what mechanical energy depends on and what it (surprisingly, maybe) does not depend on.
 
  • #3
19
0
Ok. so PEf is going to be zero, correct? and KEi is zero because the ball starts from rest. But I'm not given the mass, how can I figure out v? Do they cancel because they are constant?
 
  • #4
Filip Larsen
Gold Member
1,237
169
The mass m that enters the four terms are all the same mass, so you are right, it cancels.
 
  • #5
19
0
I got it, thanks! I appreciate the help.
 

Related Threads for: Conservation of energy of a baseball problem

Replies
6
Views
3K
  • Last Post
Replies
6
Views
7K
  • Last Post
Replies
8
Views
3K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
5
Views
4K
  • Last Post
Replies
8
Views
4K
Replies
7
Views
7K
  • Last Post
Replies
3
Views
6K
Top