Lab Quiz 6

Strangers worked for me. Symbols they use for the variables in the question is confusing tho...

and in reply to confused, maybe you had rounded off too early because the answer I got at the end without rounding off before hand is .001182

It's still not working for me either

The following steps worked out for me. This is what I did:

Wanted: Delta I= I * Delta r/ r
First find I=mg/(alpha fric+alpha) Note: take the absolute value of alpha friction.
Then, find Deta r/r = (% accuracy/100 * radius
Finally, multiply two values together.
(it's negative)

Hope it helps and will work for you guys!

Could you help me with number 3?

thank you, it's work for number 3

Yeah, tofu's suggestion for question 3 works, and remember to put the mass in kg!

I am still having trouble with Question 3

can someone plug in the numbers so we get it

Tofu your solution worked!!!!!! THANKS

You measure the moment of inertia of a wheel by measuring its angular acceleration a = 0.413 rad/s2, when applying an external torque caused by a hanging weight of mass m = 200 g as shown above. The angular acceleration is decreased by a frictional torque, accounted for by afric = - 0.193 rad/s2 in the expression for the momemt of inertia I of the wheel, I = mr(g-ra) /(|afric|+a), where r is the radius of the cylinder attached to the wheel, and g is the acceleration of gravity, which you treat as error free. You neglect the error of the accelerations a and afric, and the error of the mass m. You find out that the term (a r) in the numerator is small compared to the term g, and thus neglect its error too. What is the absolute error of I, if the 2.5 cm radius r is known with a 1.3 % accuracy. (Hint: Read in the manual of the lab, how I can be written as two factors. One factor contains the quantities assumed to be error free, after taking into account that the term (a r) can be neglected for the purpose of error calculation. Use expression (3) and (4) in "Error and Uncertainty".) Indicate with a positive (negative) sign whether, with the neglections you made above, the absolute (relative) errors of I and r are the same.

Okay for those that wanted it step by step, using tofus method this is how to do it

delta r/r = %/100 * radius (in meters) so you do (1.3/100) * .025 m = .000325

put mass into kg for this next part, and use the positive afric since it asks for absolute value
I = mg/ (|afric|+angacceleration) = (.2 g * 9.81) / (.193 + .413) = (1.962)/(.606) = 3.2376

(.000325)*(3.2376) = answer = .00105222

And it is negative

hope that helps

tofuuu thank youuu!!

what is the disk constant used for ques 2?

I'm having trouble with #2. i did .5 (m)(r^2) am I missing something.

Need help with question 2 plzz this is what I used
.5*m*r^2

Just make sure the radius is in meters and the mass is in kg. and do .5*m*r^2 ...if that doesnt work again post your question