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Find the pressure exerted on the plate by the oil and find the force

Oil of rd=0.9 is at a depth of 1m above a horiz. Rectangular plate 4m x 1m.

Im not really confident with my answers.
I got pressure exerted= 0.9x10^3

So is the force equation is hpg?

1(0.9x10^3)(9.81) = 8829N?

Or is it 4(1)(0.9x10^3)(9.81) = 35316N

Or am I completely wrong?
Reply 1
Original post by Calt4628
Oil of rd=0.9 is at a depth of 1m above a horiz. Rectangular plate 4m x 1m.

Im not really confident with my answers.
I got pressure exerted= 0.9x10^3

So is the force equation is hpg?

1(0.9x10^3)(9.81) = 8829N?

Or is it 4(1)(0.9x10^3)(9.81) = 35316N

Or am I completely wrong?


Okay I’ve tried redoing it again and got
pressure = hpg = 4(0.9x10^3)(9.81)
pressure = 35316Pa

A = 4(1) = 4m^2

and F=Ahpg = 4(35316)

which is 141264N?

please someone check this x
Original post by Calt4628
Oil of rd=0.9 is at a depth of 1m above a horiz. Rectangular plate 4m x 1m.


Original post by Calt4628
Okay I’ve tried redoing it again and got
pressure = hpg = 4(0.9x10^3)(9.81)
pressure = 35316Pa

A = 4(1) = 4m^2

and F=Ahpg = 4(35316)

which is 141264N?

please someone check this x

h is not 4m, so your pressure is wrong - it's actually the weight. Your first answer was correct for pressure (density * g * height).

If you only need the force, it's simply the weight of the oil above, i.e. density * volume * g = 0.9 * 1000 * 1 * 4 * 1 * 9.80665 N
(edited 3 years ago)
Reply 3
Original post by RogerOxon
h is not 4m, so your pressure is wrong - it's actually the weight. Your first answer was correct for pressure.

If you only need the force, it's simply the weight of the oil above, i.e. density * volume * g = 0.9 * 1000 * 1 * 4 * 1 * 9.80665 N

Thank you, so the force is 35316N?
Original post by Calt4628
Thank you, so the force is 35316N?

Yes,. The exact answer depends on what you take g as. You are also assuming an incompressible fluid.
(edited 3 years ago)
Reply 5
Thank you so much, I understand now.

If possible would you be able to check this question too please?

https://www.thestudentroom.co.uk/showthread.php?t=6425478
Reply 6
Original post by RogerOxon
Yes,. The exact answer depends on what you take g as. You are also assuming an incompressible fluid.

I’ve realised that I'm taking g=10

So the pressure is 900Pa

And Force is 900*1*4*1*10 making 36000N

Correct?
Original post by Calt4628
I’ve realised that I'm taking g=10

So the pressure is 900Pa

And Force is 900*1*4*1*10 making 36000N

Correct?

That's not correct for the pressure, which is density * g * height - you seem to have missed g.

The force is correct (with g=10 ms^-2).
Reply 8
Oh, you said that my first answer for pressure was correct, I assumed it was that. So the pressure is 9000Pa? Considering g=10?
Original post by Calt4628
Oh, you said that my first answer for pressure was correct, I assumed it was that. So the pressure is 9000Pa? Considering g=10?

Yes.

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