Calculating Force from Pole-Vaulter's Fall onto Foam-Rubber Pad

In summary, a 77 kg pole-vaulter falls from a height of 4.8 m onto a foam-rubber pad and comes to rest after 0.24 seconds. To calculate their velocity before reaching the pad, the equation Vf=gt can be used, where g is the acceleration due to gravity. To find the time (t) it takes for the vaulter to fall, kinematics or energy equations can be used. The constant force exerted on the pole-vaulter due to the collision can be calculated using the equation F=p/t, where p is the vaulter's momentum.
  • #1
mortho
100
0

Homework Statement


A 77 kg pole-vaulter falls from rest from a height of 4.8 m onto a foam-rubber pad. The pole-vaulter comes to rest 0.24 s after landing on the pad.
a)Calculate the athlete's velocity just before reaching the pad.
b)Calculate the constant force exerted on the pole-vaulter due to the collision.



Homework Equations



F=p/t

The Attempt at a Solution



for part a i did Vf=Ft/m and 755.4(0.24)/77 and got 2.35 m/s downward

for b i did F=p/t and (77)(2.35)/0.24 and got 754 N upward.

I think i calcuated the force for part a wrong and that 's why my answer was wrong.
 
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  • #2
mortho said:

Homework Statement


A 77 kg pole-vaulter falls from rest from a height of 4.8 m onto a foam-rubber pad. The pole-vaulter comes to rest 0.24 s after landing on the pad.
a)Calculate the athlete's velocity just before reaching the pad.
b)Calculate the constant force exerted on the pole-vaulter due to the collision.

...

The Attempt at a Solution



for part a i did Vf=Ft/m and 755.4(0.24)/77 and got 2.35 m/s downward

All right, one problem right off the bat is that the 0.24 seconds is the time it takes for the force from the foam pad to bring the pole-vaulter to a stop, not the amount of time it took them to fall 4.8 meters. To answer (a), you will need to calculate how long that takes.

Your equation and how you used it otherwise is fine, although a bit roundabout: you used the vaulter's weight and divided it by their mass, which gives you g. So you could have just used V_f = gt for their fall. Now you need to find t .
 
Last edited:
  • #3
For part A, keep in mind that you do not know the time it takes for him to fly until the pad, it is not .24 seconds (that is the time he is in contact with the pad itself). You can use kinematics or energy to do part A.

Part B looks right.

edit: yep ditto dynamicsolo, posted at the same time :D
 
  • #4
Oh thanks guys i figured this one right after i posted it. but thanks anyways
 

1. What is the formula for calculating constant force?

The formula for calculating constant force is F = m x a, where F is the force in Newtons (N), m is the mass in kilograms (kg), and a is the acceleration in meters per second squared (m/s2).

2. How do you calculate the force if the mass and acceleration are not given?

If the mass and acceleration are not given, you cannot calculate the force. All three variables (force, mass, and acceleration) are needed in order to use the formula for constant force.

3. Can constant force be negative?

Yes, constant force can be negative. A negative force indicates that the force is acting in the opposite direction of the positive force. For example, if a constant force of -10 N is applied to an object, it means that the force is acting in the opposite direction of the positive force, which would be 10 N.

4. How do you convert force from pounds (lbs) to Newtons (N)?

To convert force from pounds (lbs) to Newtons (N), you can use the conversion factor of 1 lb = 4.44822 N. This means that if you have a force of 10 lbs, it would be equivalent to 44.4822 N (10 x 4.44822).

5. What is the unit of measurement for force?

The unit of measurement for force is Newtons (N). However, other commonly used units for force include pounds (lbs) and kilograms (kg).

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