- #1
Ricaoma
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Homework Statement
The graph below shows the force as a function of time when a man jumps on a bathroom scale.
1) Determine the mans weight (mass, kg) using the graph.
2) Describe what happens in the time intervals A, B, C and D.
3) Determine the velocity of the man as he leaves the scale (the velocity at the beginning of his jump).
Unnecessary high resolution picture and since I have no idea how to limit the size here, I'll just link the graph instead.
http://img146.imageshack.us/img146/8286/grafq.jpg"
Homework Equations
No specific equations are given, but I'd assume the equations regarding potential energy, kinetic energy, velocity, and force would be relevant.
Though, this far I've only used
[tex]F = m×g \Leftrightarrow m = \frac{F}{g}[/tex]
to calculate an approximated mass of the man.
The Attempt at a Solution
1)
[tex]F \approx 700 N[/tex]
[tex]g \approx 9.82 m/s2 [/tex]
[tex]m \approx \frac{700}{9.82} \approx 71.3 kg[/tex]
2)
A The man starts his preparations for the jump by bending his knees. (Why does this make the force lower? Is it because of his center of mass changing?
B He re-straightens his legs, thrusting himself upwards. This makes his feet push down on the scale, making it register a higher force.
C The man is in the air and is therefore not touching the scale.
D The man lands on the scale with greater force because of the fall (related to gravity).
3)
This is were I'm stuck. At first I though about using the time he was in the air to calculate this, but I realized I didn't really know how.
Then, I changed my plan to using the force with which he thrusted himself upwards with, and using the number [tex] F = 1800N [/tex] with the formula
[tex]F = m×A \Leftrightarrow A = \frac{F}{m}[/tex]
to later be able to calculate his velocity using
[tex]V = A×\Delta T[/tex]
until I realized that I would have to assume a time and that this assumed time would be completely responsible for the result, which seems a bit to odd for an answer.
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