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

Kinetic Energy of body moving

  • Thread starter bulldog23
  • Start date
  • #1
120
0

Homework Statement



The graph below shows the net force applied to a 2.5 kg body, initially at rest but free to move along a straight line on a horizontal frictionless surface. The force acts along the same straight line.
prob37v1.gif


After the body has moved 3 m, what is it's kinetic energy?


Homework Equations


KE=1/2mv^2



The Attempt at a Solution


I just don't understand how to figure out the velocity of the body given force versus distance. Can someone explain this?
 
Last edited:

Answers and Replies

  • #2
Dick
Science Advisor
Homework Helper
26,258
618
You haven't really stated a question. But the work done on the body by a force is the integral of F*dx. And the KE of the body is (1/2)*mv^2. And the change of the kinetic energy is the work done on the body. This is the same thing we were talking about last night. Except that was the simpler case where the force was a constant. Hence mgh. F=mg, distance=h.
 
  • #3
120
0
My bad, the question is that after the body has moved 3 m, what is it's kinetic energy?
 
  • #4
120
0
How do I figure out the velocity?
 
  • #5
Dick
Science Advisor
Homework Helper
26,258
618
Was it's initial kinetic energy zero? Then the integral of the force (area under the force curve)=KE.
 
  • #6
120
0
So then I can just make squares and triangles and figure out the area right? So then I would get the KE is 4???
 
  • #7
Dick
Science Advisor
Homework Helper
26,258
618
You mean 4J, right? Always put units on things. But still not right. It would be 4J is the segment B were flat. It's not. Do make squares and triangles.
 
Last edited:
  • #8
120
0
Yeah, I meant 4 Joules. But you can separate section A and part of B into a square and the area of that is 4 J. Then you can find the area of the triangle on part B which would be 1J and then subtract part C from those. Where am I going wrong?
 
  • #9
Dick
Science Advisor
Homework Helper
26,258
618
Part C doesn't have any area. It's length is 1 and it's height is 0. 1x0=0. There is no force along section C, hence no work.
 
  • #10
120
0
Oh, I see, so that would make KE=5 J. Thanks man!
 

Related Threads on Kinetic Energy of body moving

  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
4
Views
1K
Replies
11
Views
665
Replies
3
Views
2K
Replies
0
Views
1K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
7
Views
2K
  • Last Post
Replies
8
Views
4K
  • Last Post
Replies
0
Views
2K
  • Last Post
Replies
6
Views
7K
Top