Velocity problem

  • #1
whiteruskii
2
0

Homework Statement



A pole vaulter goes 6m in the air. What is the velocity when he hits the ground?

No air resistance, just g=9.8m/s^2

Homework Equations


mgh = 1/2mv^2

Does an answer of 10.95 seem right? (I used 10m/s/s for gravity)
 
Last edited:

Answers and Replies

  • #2
denverdoc
963
0
Well, then you need another approach, maybe attending class more regularly?

I'm not being snide but for the life of me cannot think of any other method.

The one option which might not be considered strictly as kinematics is by using energy: the potential and kinetic energies under these conditions will be constant. So develop an eqn that uses both. But given the data, this is the only approach.
 
Last edited:
  • #3
whiteruskii
2
0
Well, then you need another approach, maybe attending class more regularly?

I'm not being snide but for the life of me cannot think of any other method.

The one option which might not be considered strictly as kinematics is by using energy: the potential and kinetic energies under these conditions will be constant. So develop an eqn that uses both. But given the data, this is the only approach.

Attending class would be wonderful...last week was beyond my control

anyways, not to go off on a tangent, using mgh=1/2mv^2, I canceled out mass, since it's just a multiplier to both, and got an answer of approximately 10.95. Does that seem about right?
 
  • #4
PhanthomJay
Science Advisor
Homework Helper
Gold Member
7,179
513
Attending class would be wonderful...last week was beyond my control

anyways, not to go off on a tangent, using mgh=1/2mv^2, I canceled out mass, since it's just a multiplier to both, and got an answer of approximately 10.95. Does that seem about right?
If you use an alternate approach (and yes, there is one) using the basic kinematic equation of motion
[tex]v^2 = 2gh[/tex], you arrive at the same result (same equation), even without a knowledge of energy methods. Don't forget the units for the velocity: m/s
 
  • #5
berkeman
Mentor
63,594
14,713
Yes that sounds about right. BTW, the other method would be to use the kinematic equation for distance, with the initial velocity = 0, and figure out how long it takes to travel the 6m distance in free-fall, then use that time in the velocity kinematic equation to figure out the person's velocity at that time. But your energy approach is better, because it's all contained in one easy equation.

BTW, are you guys classmates? Sounds like you have a conversation going on behind the scenes...
 
  • #6
berkeman
Mentor
63,594
14,713
Doh! PhantomJay beat me to the punch.
 

Suggested for: Velocity problem

  • Last Post
Replies
7
Views
213
Replies
7
Views
350
  • Last Post
Replies
16
Views
336
Replies
88
Views
2K
Replies
3
Views
59
Replies
12
Views
339
  • Last Post
Replies
11
Views
465
Replies
4
Views
645
Replies
2
Views
312
Replies
25
Views
471
Top