Need Physics Help(5 problems)[will rep]

**Lunatic** · 11-02-2009, 09:51 PM

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?

Iukas · 11-02-2009, 09:52 PM

1st
by the way i do not know physics at all, just wanted to be first.

**Lunatic** · 11-02-2009, 10:00 PM

Quote:

Originally Posted by Iukas

1st
by the way i do not know physics at all, just wanted to be first.

Gay

**Lunatic** · 11-02-2009, 10:06 PM

bump for title change

berserkbladex · 11-02-2009, 10:08 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?

2. .0529550685 j

sorry dude got a test tomorrow so thats all i had time for

LAballin24 · 11-02-2009, 10:10 PM

Dont remember sht from physics but here is a bump.

juju_BEAN · 11-02-2009, 10:10 PM

i have a damn physics test on friday

brb failing it, and prof. curving it so I get a C lol

Misc_Canuck · 11-02-2009, 10:11 PM

only phy 12

sawwy

**Lunatic** · 11-02-2009, 10:12 PM

Quote:

Originally Posted by berserkbladex

2. .0529550685 j

sorry dude got a test tomorrow so thats all i had time for

Didn't work

juju_BEAN · 11-02-2009, 10:12 PM

well

torque = force x lever arm (radius?)

you on the mastering physics thing?

Deathstriker666 · 11-02-2009, 10:13 PM

ill do it mann, ill edit this post when im done. edit: for q6, the radious of the sphere isnt given. So the energy cant be worked out.

**Lunatic** · 11-02-2009, 10:17 PM

Quote:

Originally Posted by juju_BEAN

well

torque = force x lever arm (radius?)

you on the mastering physics thing?

It's WebAssign. Get 4 chances to do the problem before it being counted against you.

Quote:

Originally Posted by Deathstriker666

ill do it mann, ill edit this post when im done. edit: for q6, the radious of the sphere isnt given. So the energy cant be worked out.

I copy and pasted so I dunno

ausluke · 11-02-2009, 10:19 PM

2) 0.002169648 J
havn't done physics since high school so probably isn't correct but i dunno maybe :P

**Lunatic** · 11-02-2009, 10:20 PM

I have this one worked out but it's wrong. I did it the same way my fraternity brother did it but I got it wrong and he got it right.

What is the rotational inertia of a solid iron disk of mass 47 kg, with a thickness of 6.16 cm and radius of 18.8 cm, about an axis through its center and perpendicular to it?

Any help? All other problems are done.

colt.45 · 11-02-2009, 10:21 PM

Last year I knew al this ****, now I cant remember a damn thing

**Lunatic** · 11-02-2009, 10:21 PM

Quote:

Originally Posted by ausluke

2) 0.002169648 J
havn't done physics since high school so probably isn't correct but i dunno maybe :P

**** yoooooooooooou didn't work

dantheman999 · 11-02-2009, 10:22 PM

To late to give it a shot?

Master mech eng here.

EDIT: I see the time now, seems i missed it. Theres no way anyone could have answered all those in 8 minutes, unless they work on this **** regularly. Probably take half an hour just to look up the stuff again.

Abitofmuscle · 11-02-2009, 10:22 PM

For the last one with the picture I got

A = 2.148 KN downward
B = 3.296 KN upward

I assumed that you represent the mass of the board as a concentrated force in the middle of the board.

If you use distributed forces for weights then the answers would change.

**Lunatic** · 11-02-2009, 10:22 PM

Quote:

Originally Posted by dantheman999

To late to give it a shot?

Master mech eng here.

got 37 minutes!!

colt.45 · 11-02-2009, 10:22 PM

Quote:

Originally Posted by dantheman999

To late to give it a shot?

Master mech eng here.

wat school brah?

**Lunatic** · 11-02-2009, 10:23 PM

Quote:

Originally Posted by Abitofmuscle

For the last one with the picture I got

A = 2.148 KN downward
B = 3.296 KN upward

I assumed that you represent the mass of the board as a concentrated force in the middle of the board.

If you use distributed forces for weights then the answers would change.

I ****ing love you. Repped. Care to try others?

tehmaestro · 11-02-2009, 10:24 PM

Quote:

Originally Posted by Abitofmuscle

For the last one with the picture I got

A = 2.148 KN downward
B = 3.296 KN upward

I assumed that you represent the mass of the board as a concentrated force in the middle of the board.

If you use distributed forces for weights then the answers would change.

**** I just did this one, LOL

ausluke · 11-02-2009, 10:25 PM

6a) 8.42J
if thats not right i dunno what is!

tehmaestro · 11-02-2009, 10:27 PM

6b) is 1.421m

colt.45 · 11-02-2009, 10:28 PM

Quote:

Originally Posted by ausluke

6a) 8.42J
if thats not right i dunno what is!

unless you took into account the moment of intertia its gonna be wrong.

You need the term 1/2Iw^2 as well as 1/2mv^2 in there I'm fairly sure

Abitofmuscle · 11-02-2009, 10:28 PM

Quote:

Originally Posted by Lunatic

I ****ing love you. Repped. Care to try others?

Can't figure out the others. I'm sure some misc physics guru brahs will come to help though.

ausluke · 11-02-2009, 10:29 PM

lol then its wrong

**Lunatic** · 11-02-2009, 10:29 PM

Quote:

Originally Posted by ausluke

6a) 8.42J
if thats not right i dunno what is!

Quote:

Originally Posted by tehmaestro

6b) is 1.421m

Both wrong

Deathstriker666 · 11-02-2009, 10:29 PM

Quote:

Originally Posted by Lunatic

I have this one worked out but it's wrong. I did it the same way my fraternity brother did it but I got it wrong and he got it right.

What is the rotational inertia of a solid iron disk of mass 47 kg, with a thickness of 6.16 cm and radius of 18.8 cm, about an axis through its center and perpendicular to it?

Any help? All other problems are done.

= I = 0.5m(r^2)
= 0.830584, assuming the axis is down the middle. If its like through the side

I = (1/12)m(3(r^2)+(h^2))
= 0.45987808

**Lunatic** · 11-02-2009, 10:30 PM

Quote:

Originally Posted by Deathstriker666

= I = 0.5m(r^2)
= 0.830584, assuming the axis is down the middle. If its like through the side

I = (1/12)m(3(r^2)+(h^2))
= 0.45987808

So which is the answer?