Basic physics homework

[[Tycho?]]

 

That is the graph of the velocity of the rotating object.

 

True or False:

 

A) At time t_3, the magnitude of the tangential acceleration of a point on the rim of the disc is as large as it gets.

B) According to convention, the disc rotates counter-clockwise during the interval from t_1 to t_2.

C) At time t_3, the radial acceleration of a point on the rim of the disc is zero.

D) At time t_2, the angular velocity of the disc is as large as it gets.

E) At time t_3, the magnitude of the radial acceleration of a point on the rim of the disc is as large as it gets.

F) The acceleration of a point on the rim of the disc points to the axis of the disc at time t_1.

 

I just can't get this darned thing right. I have multiple guesses since its an online assingment, but I obviously am confused about something. I've tried looking up unfamiliar terms like "tangenital acceleration" and the like, but I still get something wrong. (If I get a single wrong, I get the entire question wrong, and so I dont know which or how many individual questions I got wrong)

 

Help would be appreciated.

[mezarashi]

I'm sure this will be easy if you have the equations clarified:

 

1. tangential acceleration = change in angular velocity over time (hint: slopes of the graph)

 

2. radial acceleration = (angular velocity)^2 x radius (hint: since r is constant its proportional to the square of the angular velocity)

 

Lastly, total acceleration = radial acceleration (towards center) + tangential acceleration (tangent to rim). (hint: last question, if either is non-zero, you won't get a perfect radial or tangential vector)

[[Tycho?]]

I love you. I even tried looking up radial acceleration, but I couldn't find a concise definition, thanks a bunch.

 

If you're feeling generous you could help me with but a single other one. This one is so easy that I can't get it, and I dont know why.

 

There is an object, who's velocity changes from 3m/s to 2m/s in 4 seconds, giving an average acceleration of -0.25m/s^2. I know the accleration is correct, becuse it was the answer to a question which I got right. The mass of this object is 162 grams. What is the average force over these four seconds?

 

I get F= -0.0405 by multiplying average acceleration times mass.

 

I dont see how this is wrong, so I've tried putting in other values, dividing by 4, making it positve, just doing junk with it. I really have no idea how this is wrong, it could just be I've been working on it for so long there is something obvious that I am unable to see.

[mezarashi]

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There is an object' date=' who's velocity changes from 3m/s to 2m/s in 4 seconds, giving an average acceleration of -0.25m/s^2. I know the accleration is correct, becuse it was the answer to a question which I got right. The mass of this object is 162 grams. What is the average force over these four seconds?

 

I get F= -0.0405 by multiplying average acceleration times mass.

[/quote']

 

I don't know about this one. Using the momentum form of Newton's second law, you would still get the same answer. Maybe it's with the minus sign?

 

F x t = m x (change in velocity)

 

But honestly your answer seems correct... oh, and you're welcome