Estimate how fast he should be moving

  • Thread starter Thread starter WillParadigm
  • Start date Start date
  • Tags Tags
    Estimate
AI Thread Summary
The discussion revolves around calculating the initial velocity Superman needs to clear Disque Hall, estimated at 160 feet tall. Participants clarify the use of kinematic equations, particularly how to relate initial velocity, time, and acceleration due to gravity (32.2 ft/s²). The key equation discussed is d = v(i)t + 1/2at², where the challenge lies in determining time (t) without prior knowledge of it. The solution involves recognizing that at maximum height, Superman's final velocity is zero, allowing for the calculation of time based on initial velocity. Ultimately, the conversation emphasizes the importance of substituting the time expression back into the distance equation to find the required initial velocity.
WillParadigm
Messages
16
Reaction score
0
Kinematics Problem. How do I get T to solve for V(i). PLEASE HELP

9.Superman is supposed to leap tall buildings in a single bound. Suppose that he obeys the normal laws of physics in this feat. Estimate how fast he should be moving when he leaves the ground so that he just clears the top of Disque Hall. (Hint # 1: how fast would he be moving if he just fell off the top? Hint #2: you have to estimate how tall Disque Hall is.)

Disque Hall is I estimate about 160 feet tall.

with hint #1, I mean, I know g=9.8 m/s^2 but how do I use that to help me figure out how fast he should be going to over leap the building?

Please help me!

*edit, alright, I mean, I know this equation is

d=v(i)t + 1/2at^2

so I have d, which is 160 feet, I have a, which is 9.8 m/s^2, but I converted that into feet to match the building, so a, is now 32.2 ft/s^2. and I know I'm trying to solve for the initial velocity, which has to be great enough so that he can jump over the building, but how do I find t? am I supposed to just guess how long it'll take him?! because then I would know all the variables, but that doesn't seem right
 
Last edited:
Physics news on Phys.org
ok reedited, so I know what I'm looking for, but the question is, how do I determine how to find them, what equation am I missing?
 
1. Find out when superman reaches maximum height (what must his velocity be then?)
2. Use the time found here in your distance equation.
This yields an equation for the initial velocity
 
ok, I can understand that part for finding time, superman's final height

g = 9.8 m/s² and upward velocity is negative, since the gravitational acceleration, which acts downward, is always positive. so when superman reaches his maximum height, his velocity should be zero. right? So, vf = 0.

vf = vi + at
0 = vi + (9.8 m/s²)t

and that's all I got, do I already start estimating how fast he should be going at vi to get t? but then that doesn't make sense, since you need t in the other equation to get vi, so this is what is confusing me
 
You have, with correct sign:
0=v_{i}-gt_{f}
whatever initial velocity (v_{i}) is, and whatever the "final" time is.
Hence, you have:
t_{f}=\frac{v_{i}}{g}
Substitute this expression for the final time into the "t"-place in your distance equation.
 
are you a physics professor/major? because you should be... =)

thank you very much, that makes 100% sense now.
 
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 'Correct statement about a reservoir with an outlet pipe'
The answer to this question is statements (ii) and (iv) are correct. (i) This is FALSE because the speed of water in the tap is greater than speed at the water surface (ii) I don't even understand this statement. What does the "seal" part have to do with water flowing out? Won't the water still flow out through the tap until the tank is empty whether the reservoir is sealed or not? (iii) In my opinion, this statement would be correct. Increasing the gravitational potential energy of the...
Back
Top