Conceptual physics homework, easy, but understanding

AI Thread Summary
Bronco Brown's bungee jumping scenario involves calculating the change in momentum (∆mv) during a 2-second interval after free-falling for 3 seconds. Initially, his momentum after the free fall is approximately 2943 kg*m/s, not 3000 kg*m/s as rounded. The change in momentum during the slowing down phase is calculated using the impulse-momentum theorem, resulting in a ∆mv of -2943 kg*m/s. The discussion highlights the importance of accurately determining initial conditions and applying the correct equations. Understanding these concepts is crucial for solving similar physics problems effectively.
knnox
Messages
2
Reaction score
0

Homework Statement


Bronco Brown wants to put Ft =∆mv to
the test and try bungee jumping. Bronco
leaps from a high cliff and experiences
free fall for 3 seconds. Then the bungee
cord begins to stretch, reducing his speed
to zero in 2 seconds. Fortunately, the cord
stretches to its maximum length just short
of the ground below.

Homework Equations



∆mv at 3-s free fall is 3000 kg m/s
Then the question asks: ∆mv during the 2-s interval of slowing
down

The Attempt at a Solution



To my knowledge it is at final velocity leaving it at 3000 kg*m/s
Would it be 1500kg m/s or 3000kg m/s?
I think 3000, but I'm not sure the equation to understand it.
The equation I used gave me 1500 because of the slowing down.
Please help me understand this better.
 
Physics news on Phys.org
Welcome to PF knnox!

You are not communicating particularly well, I'm afraid. Nowhere in your problem statement does it actually state what you are supposed to work out. If the problem is to figure out "delta mv during the 2-second interval of slowing down", then that's fine, but I don't know how to check your work, because I don't see a mass stated for Bronco Brown anywhere.
 
cepheid said:
Welcome to PF knnox!

You are not communicating particularly well, I'm afraid. Nowhere in your problem statement does it actually state what you are supposed to work out. If the problem is to figure out "delta mv during the 2-second interval of slowing down", then that's fine, but I don't know how to check your work, because I don't see a mass stated for Bronco Brown anywhere.

I apologize, it is 100kg, but looking back over this I now realize its just ask delta mv during the 2-s interval which is just 3000kg*m/s which is the same as impulse. Thank you for the response though and sorry for my lack of communication!
 
knnox said:
I apologize, it is 100kg, but looking back over this I now realize its just ask delta mv during the 2-s interval which is just 3000kg*m/s which is the same as impulse. Thank you for the response though and sorry for my lack of communication!

You can figure out his speed after free-falling for three seconds using v = v0 - gt, where v0 = 0, since he starts from rest at the beginning of the fall. I get 29.43 m/s for that, which when multiplied by 100 kg gives you a momentum of 2943 kg*m/s. (I guess you rounded up to 3000, but this introduces error). After that, you need to use the impulse-momentum theorem:

FΔt = Δ(mv)​

Here, Δ(mv) will be -2943 m/s, since he starts with 2943 kg*m/s, and ends with 0 kg*m/s, so the change in momentum is 0 - 2943.

Now, given Δ(mv), you can solve for F in Newtons, given that the impulse occurred over a time interval of Δt = 2 seconds.

It sounds like you had it right (up to rounding error) in the first place.
 
Thread 'Voltmeter readings for this circuit with switches'
TL;DR Summary: I would like to know the voltmeter readings on the two resistors separately in the picture in the following cases , When one of the keys is closed When both of them are opened (Knowing that the battery has negligible internal resistance) My thoughts for the first case , one of them must be 12 volt while the other is 0 The second case we'll I think both voltmeter readings should be 12 volt since they are both parallel to the battery and they involve the key within what the...
Thread 'Struggling to make relation between elastic force and height'
Hello guys this is what I tried so far. I used the UTS to calculate the force it needs when the rope tears. My idea was to make a relationship/ function that would give me the force depending on height. Yeah i couldnt find a way to solve it. I also thought about how I could use hooks law (how it was given to me in my script) with the thought of instead of having two part of a rope id have one singular rope from the middle to the top where I could find the difference in height. But the...

Similar threads

Back
Top