# Exam III Practice Problems (liquids and pressures)

1. Apr 20, 2006

### Alt+F4

hi, i got an exam soon and i need help with a couple of problems

http://online.physics.uiuc.edu/cgi/courses/shell/phys101/spring06/prep2a.pl?practice/exam3/sp05 [Broken] Question 7.

How would i find the tension i know that i must use Bernoulli equation but what would i be solving for

Last edited by a moderator: May 2, 2017
2. Apr 20, 2006

### dav2008

What are the forces acting on the block?

Can you draw a free body diagram of the block?

The Bernoulli equation is for fluid flow so I'm not sure why (or how) you would use it here.

3. Apr 20, 2006

### Alt+F4

ooo well all i have been doing for the past 4 weeks is using that eqaution for HW and stuff so i thought it must be it. Anywyas, You have the Water pushing up, Wood Pushing down and String pulling down

4. Apr 20, 2006

### dav2008

Right. You have the buoyant force acting upwards, the weight of the block acting downwards and tension acting downwards.

Can you see how to solve for tension now?

5. Apr 20, 2006

### Alt+F4

Edit:Never mind

6. Apr 20, 2006

### dav2008

You are given the volume of the block and its density. Using those facts you can find its mass.

As far as the forces, like you said earlier there are only 3 forces: Tension down, weight down, and buoyancy up.

Recall Archimedes' principle that the buoyancy force is equal to the weight of the displaced fluid.

7. Apr 20, 2006

### Alt+F4

thanks, I'll be back with more in 5 min. :)

8. Apr 20, 2006

### Alt+F4

ya i got it, there are too many stuff that are same like V= Velocity but then it is Volume in that equation. Crazy

9. Apr 20, 2006

### Alt+F4

http://online.physics.uiuc.edu/cgi/courses/shell/phys101/spring06/prep2a.pl?practice/exam3/sp05 [Broken] Question 15. ANy trick to finding the quick answer to these. Thanks

Last edited by a moderator: May 2, 2017
10. Apr 20, 2006

### dav2008

Well given that it's a multiple choice you can just see which one of those three equations fits your given information.

You're given that at t=0 s v=11.1 m/s.

11. Apr 20, 2006

### Alt+F4

Thanks alot, i need to ace this exam so sorry for all the questions.

http://online.physics.uiuc.edu/cgi/courses/shell/phys101/spring06/prep2a.pl?practice/exam3/sp05 [Broken] Question 16

Can i use one of these equations for 15 to just plug in 1.5 and get the V which i can get Kinetic energy from

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12. Apr 20, 2006

### dav2008

Well try it and see if you get the right answer.

13. Apr 20, 2006

### Alt+F4

:( nope well i was thinking of using X(t) = A cost(omega t) but what would A be hmmmm

14. Apr 20, 2006

### Alt+F4

Im stupid. I got it

Last edited: Apr 20, 2006
15. Apr 20, 2006

### Alt+F4

http://online.physics.uiuc.edu/cgi/courses/shell/phys101/spring06/prep2a.pl?practice/exam3/sp05 [Broken] Question 19. I am not getting why Pa > Pb. Thinking of it B is a more tighter area so there will be more pressue on it

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16. Apr 20, 2006

### Alt+F4

http://online.physics.uiuc.edu/cgi/courses/shell/phys101/spring06/prep2a.pl?practice/exam3/fa04 [Broken] Question 7. SO what i did was

Force of Friction - Force of compression of spring
UkMg - -kx = 0
(X)(20*9.8) = 270 * .2

What am i doing wrong.

Last edited by a moderator: May 2, 2017
17. Apr 20, 2006

### Alt+F4

Question 25 http://online.physics.uiuc.edu/cgi/courses/shell/phys101/spring06/prep2a.pl?practice/exam3/fa04 [Broken]

Okay so i got the answer to 24 which was 600. FOR 25 i am going to use this formula h = (M + m)/ (Density* A)

D= M/v
600 = M/ (2*.15) or is it (2*.25)
little m is just 20*3 = 60
Density on bottom is 1000
A = .25*2
plug that it and i am not getting the answer

Last edited by a moderator: May 2, 2017
18. Apr 20, 2006

### Alt+F4

http://online.physics.uiuc.edu/cgi/courses/shell/phys101/spring06/prep2a.pl?practice/exam3/fa05 [Broken] Question 10. hmmmmmmm Well wat i did was

(1000)(9.8)(.3) = (X)(9.8)(.6)
Which gave me 500 which is wrong.

Last edited by a moderator: May 2, 2017
19. Apr 20, 2006

### Alt+F4

http://online.physics.uiuc.edu/cgi/courses/shell/phys101/spring06/prep2a.pl?practice/exam3/fa05 [Broken] Question 19. I think this should be it for a while, Thanks for everyones help.

So what i did was

Patm = P1 + .5(1000)(2^2) + (1000*9.8*2)
Which gives me

Patm - PB = 2.2*10^4 (not the answer)