#1
UG i need help with a bit of physics since i dont understand it,if someone could explain it to me id be very grateful.

A diver of mass 80kg climbs to the top of a 5m platform

What is his speed as he hits the water?

If someone could explain it?
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#5
suvat my friend lol.

initial speed (u)=0
acceleration (a)=-9.81 (due to gravity)
final velocity (v)=?
distance (s)= 5

(vxv)=(uxu)+2as

Easy
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Quote by darkstar2466
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#6
I don't understand what you mean by "speed". Kinetic energy? Velocity?

Edit - Nevermind, Got it, and to the guy who found the GPE first, that's the way that I do it,
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Last edited by Aaron0612 at Apr 9, 2008,
#7
potential energy = mass x gravity x height

Mass = 80kg
Gravity on earth = 10N
Height = 5m

Gravitational Potential Energy = 4000N for the guy... now just work out the speed.

edit: nvm i might have been wrong
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#8
Quote by notsojoeyb4eva
suvat my friend lol.

initial speed (u)=0
acceleration (a)=-9.81 (due to gravity)
final velocity (v)=?
distance (s)= 5

(vxv)=(uxu)+2as

Easy



damn I forgot about that, but they should yield the same result
#9
Quote by Rocking-Rob
damn I forgot about that, but they should yield the same result


Yeah i forgot about your equation as well, yours would make more sense though considering he's been given the weight in the question.

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Quote by darkstar2466
WRONG.

The only reason it exists is because drugs get people fucked up, and people love getting fucked up.

#10
Quote by notsojoeyb4eva
suvat my friend lol.

initial speed (u)=0
acceleration (a)=-9.81 (due to gravity)
final velocity (v)=?
distance (s)= 5

(vxv)=(uxu)+2as

Easy


There is a much easier way, but I guess that would work. I'm trying to remember it, we did it in like 6th grade science class, .
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#11
The mass doesn't matter... Objects fall in space relative to their air resistance and the constant of acceleration of gravity (9.8 m/s/s or 16 f/s/s on earth)... i would assume that you are supposed to disregard the air resistance because it's practically impossible to tell with this information... You have to work around algebraically with the equation H(t)=-9.8 t(squared) + (velocity at start) (t) + (original height at start) T = time
its actually kind of a hard question and i'm not going to work it out all the way but you use the above information

edit: sorry -4.9t (squared) because its 1/2acceleration
Last edited by Travlembo at Apr 9, 2008,
#12
Quote by notsojoeyb4eva
Yeah i forgot about your equation as well, yours would make more sense though considering he's been given the weight in the question.


thats brilliant you 2,that makes sense now,thanks alot
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#13
speed is average time*distance
distance is known, 5m
acceleration due to gravity is 9.8m/(second*second)
Every second, until he covers the 5m, he'll be accelerating at a rate of 9.8m.
His weight doesn't matter, since all objects fall at the same rate.

Hope that helped a bit.
There's a solution, but I haven't been in school for weeks.
#14
I get 9.9m/s which is a reasonable value.
D-U-F-R-A-I-S


Quote by darkstar2466
WRONG.

The only reason it exists is because drugs get people fucked up, and people love getting fucked up.

#15
Quote by notsojoeyb4eva
suvat my friend lol.

initial speed (u)=0
acceleration (a)=-9.81 (due to gravity)
final velocity (v)=?
distance (s)= 5

(vxv)=(uxu)+2as

Easy


The man has it, although you'd leave acceleration due to gravity as a positive value

Although the other guy had the correct energy equations
#16
You can say that in this situation, his gravitational potential energy is converted to kinetic energy as he falls:

GPE = KE
mgh = 1/2 m v^2

the mass can be cancelled from either side to make
gh = 1/2 v^2

rearranging gives
v^2 = 2gh

and finally v = square root of 2gh, where g is acceleration due to gravity(9.81ms^-2) and h is how far he falls(5m). That should work.

Quote by Oblivion_Rps
Gravitational Potential Energy = 4000N

Energy is measured in joules, not newtons

EDIT: The suvat equations will also work, because when talking about speeds of objects, the mass is irrelevant since falling objects all fall at the acceleration provided by gravity.
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Last edited by The Overlord at Apr 9, 2008,
#17
x(distance)=Vi(initial velocity)*T(time) + 1/2 A(accelleratoin)*T(time)^2

so you're initial velocity will be 0 since he is starting from rest....

distance = .5 accelleration * time^2

acelleratoin of gravity is 9.8, say 10 in the negative direction since he is going down

now plug in your height for distance and solve
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#18
the answer is 10

both me and notsojoeyb4eva have given ways to work it out

potential energy = mass x gravity x height

energy = 1/2 mass x velocity^2

heres what you do

gravity is 9.81 (but i'll use 10 as I'm doing it in my head), his mass is 80 and the height is 5m

work out the PE, 10x80x5 = 4000

PE and energy are the same thing so sub into

energy = 1/2 mass x velocity^2

4000 - 0.5 x 80 x v^2

rearange to get 100 = v^2

v = 10 m/s
#20
I did both the energy way, and the "suvat" way, just to make sure and both give the answer

(10g)^0.5

Where g is whatever graviation constant you use, (10, 9.8, 9.81, whatever)