Finding Momentum w/ Mass and Height

In summary, a 62.0 kg male dancer leaps 0.31 m high and reaches the ground with a momentum of kgm/s. To stop the dancer, an impulse of Ns is needed. As the dancer lands and his knees bend, the stopping time is extended to 0.050 s. Using the kinematic equations, the average force exerted on the dancer's body can be calculated in N. The stopping force can then be compared to the dancer's weight to determine the impact of the landing.
  • #1
duke1
14
0
Okay sry for the first thread it wasn't really detailed.

A 62.0 kg male dancer leaps 0.31 m high.
(a) With what momentum does he reach the ground?
kgm/s
(b) What impulse is needed to stop the dancer?
Ns
(c) As the dancer lands, his knees bend, lengthening the stopping time to 0.050 s. Find the average force exerted on the dancer's body.
N
(d) Compare the stopping force with his weight.
(stopping force/dancer's weight)

So the main problem is I can't find any worked out examples of these problems in our book. I may be wrong but I just don't see how to find momentum without another bit of information besides hieght and mass. So I'm stuck and don't even really know where to start trying to work it out. There is a time given in C but it doesn't apply yet to A.

Any ideas?? Help is really appreciated.

bp
 
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  • #2
Oh! I thought that the dancer's height was given! (As in, a 5' 11", 195 lb dancer...)

At the top of the dancer's leap (given) what is the y-component of his velocity?
With what velocity will he hit the ground? (think free fall)
 
  • #3
duke1 said:
Okay sry for the first thread it wasn't really detailed.

A 62.0 kg male dancer leaps 0.31 m high.
(a) With what momentum does he reach the ground?
kgm/s
(b) What impulse is needed to stop the dancer?
Ns
(c) As the dancer lands, his knees bend, lengthening the stopping time to 0.050 s. Find the average force exerted on the dancer's body.
N
(d) Compare the stopping force with his weight.
(stopping force/dancer's weight)

So the main problem is I can't find any worked out examples of these problems in our book. I may be wrong but I just don't see how to find momentum without another bit of information besides hieght and mass. So I'm stuck and don't even really know where to start trying to work it out. There is a time given in C but it doesn't apply yet to A.

Any ideas?? Help is really appreciated.

bp
The key is to find the dancer's velocity just before the dancer hits the ground. There are a couple of ways to do this, using motion equations or conservation of energy, that relate height, velocity, and the acceleration of gravity. Can you pick one?
 
  • #4
ok...so 9.8 is free fall but how can i use that without another time or something? I am sure I am missing something simple
 
  • #5
duke1 said:
I am sure I am missing something simple
yup!:smile:
Do you remember your basic equations for motion with constant acceleration?
 
  • #6
ok thanks a lot...the hint really helped so i picked out one of the kinematics we got in class...thx for the help
 
  • #7
(b) What impulse is needed to stop the dancer?
Ns

How do you find this? Isn't Impulse equal to Force multiplied by time and you don't know the time?
 
Last edited:
  • #8
Duke1, please show us how much of it you can work out now.
 
  • #9
americanforest said:
How do you find this? Isn't Impulse equal to Force multiplied by time and you don't know the time?

I used the kinematic equations...Final Velocity Squared=Distance x acceleration (.31 x 9.8 =V) then multiplied that b/c it was the change in V times the mass...got impulse
 
  • #10
verty said:
Duke1, please show us how much of it you can work out now.

I've worked out and finished this one now.
 
  • #11
verty said:
Duke1, please show us how much of it you can work out now.

I've worked out and finished this one now.
 
  • #12
verty said:
Duke1, please show us how much of it you can work out now.

I've worked out and finished this one now.
 
  • #13
verty said:
Duke1, please show us how much of it you can work out now.

I've worked out and finished this one now.
 

1. What is momentum?

Momentum is a measure of an object's motion, determined by its mass and velocity. In simple terms, it is the quantity of motion that an object possesses.

2. How is momentum related to mass and height?

Momentum is directly proportional to an object's mass and velocity. In the case of finding momentum with mass and height, the height refers to the object's potential energy, which is converted into kinetic energy as the object gains velocity while falling.

3. What is the formula for finding momentum with mass and height?

The formula for finding momentum with mass and height is p = mgh, where p is momentum, m is mass, g is the acceleration due to gravity, and h is the height of the object.

4. How does changing the mass or height affect momentum?

Changing the mass or height will directly affect the momentum of an object. Increasing the mass or height will result in a higher momentum, while decreasing either will result in a lower momentum.

5. What is the significance of finding momentum with mass and height in science?

Finding momentum with mass and height is important in many scientific fields, such as physics and engineering. It helps us understand the relationship between an object's mass, height, and its motion, and allows us to make predictions and calculations in various real-world scenarios.

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