Calculus heavy physics problem

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Oct 10th 2011, 07:59 PM
CrusaderKing1

Calculus heavy physics problem

A 5.00 http://session.masteringphysics.com/render?units=kg crate is suspended from the end of a short vertical rope of negligible mass. An upward force http://session.masteringphysics.com/render?tex=F%28t%29 is applied to the end of the rope, and the height of the crate above its initial position is given by http://session.masteringphysics.com/...2Funits%3E%29t +(0.61 http://session.masteringphysics.com/...nits=m%2Fs%5E3)http://session.masteringphysics.com/render?tex=t%5E3

What is the magnitude of the force http://session.masteringphysics.com/render?tex=F when 3.60 http://session.masteringphysics.com/render?units=s?

Alright, I have done about 20 physics problems that are due next week, and this is the last one. It is very heavy on calculus, which i am not good at. In fact, I don't even really know where to start on this one. Thanks for the help.
Oct 11th 2011, 03:09 AM
skeeter

Re: Calculus heavy physics problem

Quote:

Originally Posted by CrusaderKing1

A 5.00 http://session.masteringphysics.com/render?units=kg crate is suspended from the end of a short vertical rope of negligible mass. An upward force http://session.masteringphysics.com/render?tex=F%28t%29 is applied to the end of the rope, and the height of the crate above its initial position is given by http://session.masteringphysics.com/...2Funits%3E%29t +(0.61 http://session.masteringphysics.com/...nits=m%2Fs%5E3)http://session.masteringphysics.com/render?tex=t%5E3

What is the magnitude of the force http://session.masteringphysics.com/render?tex=F when 3.60 http://session.masteringphysics.com/render?units=s?

Alright, I have done about 20 physics problems that are due next week, and this is the last one. It is very heavy on calculus, which i am not good at. In fact, I don't even really know where to start on this one. Thanks for the help.

$y(t) = 2.80t + 0.61t^3$

surely you know how to take derivatives of polynomial expressions ...

$a(t) = y''(t)$

$F(t) = m \cdot a(t)$
Oct 11th 2011, 07:47 AM
CrusaderKing1

Re: Calculus heavy physics problem

Quote:

Originally Posted by skeeter

$y(t) = 2.80t + 0.61t^3$

surely you know how to take derivatives of polynomial expressions ...

$a(t) = y''(t)$

$F(t) = m \cdot a(t)$

Yes, If the question said use the derivative, and then find F(t), I would have understood it. I am very bad at starting problems!

Ok, I did derive the function and received 20.6848 for acceleration, with then multiplied by 5.00 kg = 103.424

Would the units be in N? Probably N right? Yes, I'm not very good at this yet.

Thanks for your help! Much appreciated.
Oct 11th 2011, 10:35 AM
skeeter

Re: Calculus heavy physics problem

Quote:

Originally Posted by CrusaderKing1

Yes, If the question said use the derivative, and then find F(t), I would have understood it. I am very bad at starting problems!

Ok, I did derive the function and received 20.6848 for acceleration, with then multiplied by 5.00 kg = 103.424

Would the units be in N? Probably N right? Yes, I'm not very good at this yet.

Thanks for your help! Much appreciated.

incorrect

$a(6) = 21.96 \, m/s^2$ ... recheck your calculations

at this level of calculus-based physics, you are expected to know the relationship between position, velocity, and acceleration ...

$v(t) = y'(t)$

$a(t) = v'(t) = y''(t)$
Oct 11th 2011, 11:26 AM
CrusaderKing1

Re: Calculus heavy physics problem

Quote:

Originally Posted by skeeter

incorrect

$a(6) = 21.96 \, m/s^2$ ... recheck your calculations

at this level of calculus-based physics, you are expected to know the relationship between position, velocity, and acceleration ...

$v(t) = y'(t)$

$a(t) = v'(t) = y''(t)$

65.88 N

I didn't realize that I need to derive the function twice.

I have calculus and physics this semester, and had only high school trig. before 5 weeks ago.

The value is definitely right, but the program(masteringphysics) won't accept "N" as the correct units.

would kg*m/s2 work?

Thanks.
Oct 11th 2011, 12:59 PM
skeeter

Re: Calculus heavy physics problem

Quote:

Originally Posted by CrusaderKing1

65.88 N

I didn't realize that I need to derive the function twice.

I have calculus and physics this semester, and had only high school trig. before 5 weeks ago.

The value is definitely right, but the program(masteringphysics) won't accept "N" as the correct units.

would kg*m/s2 work?Thanks.

Not being familiar with what the "machine" wants, I can't really say ... it's worth a shot.
Oct 11th 2011, 01:05 PM
CrusaderKing1

Re: Calculus heavy physics problem

Quote:

Originally Posted by skeeter

Not being familiar with what the "machine" wants, I can't really say ... it's worth a shot.

yes, I guess so.