Need Physics Help(5 problems)[will rep] - Page 2

ausluke · 11-02-2009, 10:31 PM

oh god i got 14.23m for 6b no wonder i did so crap in physics last year

**Lunatic** · 11-02-2009, 10:31 PM

That's wrong. THat's the same as 8.42.

ausluke · 11-02-2009, 10:33 PM

yeah ah well your better of asking this in a physics forum
unless you're having any troubles with VB.NET i can't help you

dantheman999 · 11-02-2009, 10:34 PM

Number 2 should be 48.106 watts

About 99% positive.

Edit, may have messed up units. Anyone know if i keep the moment of ineteria in KG or grams.

LAballin24 · 11-02-2009, 10:36 PM

I used to get help from this forum so much for hw.

http://www.physicsforums.com/

Deathstriker666 · 11-02-2009, 10:36 PM

2) = 5.06x10(-3)

5) a) = 126136.5075
b) 23889.49006 each kid

i cant do 6 but i might need some persuasion, and i have to go to a poo.

ex3e1989 · 11-02-2009, 10:37 PM

Quote:

Originally Posted by Lunatic

6. A solid sphere of mass 0.604 kg rolls without slipping along a horizontal surface with a translational speed of 5.28 m/s. It comes to an incline that makes an angle of 38? with the horizontal surface. Neglect energy losses due to friction.

(a) What is the total energy of the rolling sphere?

(b) To what vertical height above the horizontal surface does the sphere rise on the incline?

for a) the TOTAL kinetic energy will be K-translation + K-rotational
so Ktotal = 0.5mv^2 + 0.5Iw^2
I = moment of inertia
w=angular velocity

maybe someone can figure it out, i forgot how to find them :<
u sure u aren't given any more info for 6?

ausluke · 11-02-2009, 10:37 PM

Quote:

Originally Posted by LAballin24

I used to get help from this forum so much for hw.

http://www.physicsforums.com/

wow wish i knew about this site last year

dantheman999 · 11-02-2009, 10:41 PM

Quote:

Originally Posted by ex3e1989

for a) the TOTAL kinetic energy will be K-translation + K-rotational
so Ktotal = 0.5mv^2 + 0.5Iw^2
I = moment of inertia
w=angular velocity

maybe someone can figure it out, i forgot how to find them :<
u sure u aren't given any more info for 6?

6 shoudl be easy, except im struggling to find the moment of inertia without the radious of the ball.

tehmaestro · 11-02-2009, 10:41 PM

9. is

107.78 rad/s

or

17.15 hz

FFF if that doesn't work:

107.7 rad/s

or

17.1414 hz

just some different rounding

ex3e1989 · 11-02-2009, 10:43 PM

Quote:

Originally Posted by dantheman999

6 shoudl be easy, except im struggling to find the moment of inertia without the radious of the ball.

yes u need either the density of the ball or the radius to figure out 6 if rotational KE is being considered

dantheman999 · 11-02-2009, 10:46 PM

Quote:

Originally Posted by ex3e1989

yes u need either the density of the ball or the radius to figure out 6 if rotational KE is being considered

yeah pretty much, somethign has to be missing. Unless you treat it as a point mass and just use its linear KE. Which is stupid.

dantheman999 · 11-02-2009, 10:47 PM

Quote:

Originally Posted by colt.45

wat school brah?

U of Ottawa.

mmbenani · 11-02-2009, 10:47 PM

Quote:

Originally Posted by Lunatic

Don't care about the work being showed right now. I just need answers by 11:59

The fifth question is attached and includes a picture. Will rep for correct answers.

2. How much work is done by the motor in a CD player to make a CD spin, starting from rest? The CD has a diameter of 12.2 cm and a mass of 15.6 g. The laser scans at a constant tangential velocity of 1.14 m/s. Assume that the music is first detected at a radius of 19.8 mm from the center of the disk. Ignore the small circular hole at the CD's center.

5. A playground merry-go-round made in the shape of a solid disk, has a diameter of 2.64 m and a mass of 350.1 kg. Two children, each of mass 30.0 kg, sit on opposite sides at the edge of the platform. Approximate the children as point masses.

(a) What torque is required to bring the merry-go-round from rest to 29 rpm in 19.5 s?

(b) If two other bigger children are going to push on the merry-go-round rim to produce this acceleration, with what force magnitude must each child push?

6. A solid sphere of mass 0.604 kg rolls without slipping along a horizontal surface with a translational speed of 5.28 m/s. It comes to an incline that makes an angle of 38? with the horizontal surface. Neglect energy losses due to friction.

(a) What is the total energy of the rolling sphere?

(b) To what vertical height above the horizontal surface does the sphere rise on the incline?

9. A uniform disk with a mass of 815 g and radius 17.0 cm is rotating on frictionless bearings with an rotational speed of 18.0 Hz when Jill drops a 105 g clod of clay on a point 7.50 cm from the center of the disk, where it sticks. What is the new rotational speed of the disk?

Alot of the time if you google these online assignments, people have asked and got the answer to the exact question on yahoo answers or some shyt.. jus sayin.

**Lunatic** · 11-02-2009, 10:47 PM

Quote:

Originally Posted by dantheman999

Number 2 should be 48.106 watts

About 99% positive.

Edit, may have messed up units. Anyone know if i keep the moment of ineteria in KG or grams.

Gotta be Joules.

Repped for #9

**Lunatic** · 11-02-2009, 10:48 PM

Quote:

Originally Posted by mmbenani

Alot of the time if you google these online assignments, people have asked and got the answer to the exact question on yahoo answers or some shyt.. jus sayin.

We all have different numbers and most aren't on there.

mmbenani · 11-02-2009, 10:50 PM

I thought it was mastering physics lols, my bad

ex3e1989 · 11-02-2009, 10:52 PM

6a)

try this:

=11.78699

dantheman999 · 11-02-2009, 10:52 PM

Quote:

Originally Posted by Lunatic

Gotta be Joules.

Repped for #9

Sorry, its joules, it should be right.

exact answer in calc is 48.10648209 joules

Let me know if thats right, ill redo the numbers if not since the work is very straitforward.

Its just

W= 1/2 * I * w^2

Where
w=V/r

I=1/2 *m * R^2

W is work
V is tangental velocit
I is moment of intertia
r is radious of laser
R is disk radius
M is disk mass

tehmaestro · 11-02-2009, 10:52 PM

Quote:

Originally Posted by Lunatic

Gotta be Joules.

Repped for #9

Thanks, I tried my best at the other ones but really have no clue. It's been 2 years since I've had to do problems like these, sorry :|

Mr_dingleberries · 11-02-2009, 10:54 PM

How much time do you have?

Im attempting #5 - gimme a few minutes!

**Lunatic** · 11-02-2009, 10:55 PM

Quote:

Originally Posted by ex3e1989

6a)

try this:

=11.78699

Yup. Repped

Quote:

Originally Posted by dantheman999

Sorry, its joules, it should be right.

exact answer in calc is 48.10648209 joules

Let me know if thats right, ill redo the numbers if not since the work is very straitforward.

Its just

W= 1/2 * I * w^2

Where
w=V/r

I=1/2 *m * R^2

W is work
V is tangental velocit
I is moment of intertia
r is radious of laser
R is disk radius
M is disk mass

Say check syntax of error

**Lunatic** · 11-02-2009, 10:55 PM

Quote:

Originally Posted by bs3

How much time do you have?

Im attempting #5 - gimme a few minutes!

4 minutes :/

dantheman999 · 11-02-2009, 10:57 PM

Quote:

Originally Posted by Lunatic

Yup. Repped

Say check syntax of error

What?

Mr_dingleberries · 11-02-2009, 10:57 PM

Quote:

Originally Posted by Lunatic

4 minutes :/

fuuuuuuuuuuuuuu

hold on a second

**Lunatic** · 11-02-2009, 10:58 PM

Quote:

Originally Posted by dantheman999

What?

Dunno. It was wrong with "Check syntax of your error" as explanation.

dantheman999 · 11-02-2009, 10:59 PM

Quote:

Originally Posted by Lunatic

Dunno. It was wrong with "Check syntax of your error" as explanation.

try 0.048106 quick!

Mr_dingleberries · 11-02-2009, 11:00 PM

Yo for #5

well as far as I know, approximating the children as point masses means that they can just be considered as point and the dimensions of the children don't matter. Im not sure much can be done with the question if that is all the information given, but im tryin

**Lunatic** · 11-02-2009, 11:00 PM

Too late

ex3e1989 · 11-02-2009, 11:00 PM

since u dont have much time...here is a semi-guess for 6b)
1.98926