Physics, 01.08.2019 12:00 paulstanley972

The path of motion of a 8-lb particle in the horizontal plane is described in terms of polar coordinates as r = (2 t + 1)ft and θ = (0.2 t2 − t) rad, where t is in seconds.

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Answer from: jay0630

Missing question in the text:
"Determine the magnitude of the resultant force acting on the particle when t=2s."

For Newton's second law, the force is given by
F=ma

where m is the mass of the particle and a its acceleration.

The acceleration in polar coordinates is given by:
$a= \sqrt{a_r^2+a_{\theta}^2}$
where
$a_r = r''-r \theta'^2$
$a_{\theta} = r \theta'' +2r'\theta '$
are the radial and tangential accelerations.

Therefore, to find the acceleration starting from the polar coordinates, we need to find the derivatives of r and $\theta$ . Let's compute them:
r=2t+1

We need the values at t=2s, therefore we have
r=5 ft=1.52 m

and
$\theta = 0.2 t^2-t$
$\theta' = 0.4t-1$
$\theta''=0.4$
And using t=2s,
$\theta = -1.2 rad$
$\theta' = -0.2 rad$
$\theta''=0.4 rad$

And now we can calculate the acceleration:
$a_r=r''-r\theta '^2 =-0.06$
$a_{\theta}=r\theta ''+2r' \theta ' = 0.36$
and
$a= \sqrt{a_r^2+a_{\theta}^2}= \sqrt{(-0.06)^2+(0.36)^2}=0.35 m/s^2$
And using the mass:
m=8 lb=3.63 kg

we find the force:
$F=ma=3.63 kg\cdot 0.35 m/s^2=1.29 N$

Answer from: Quest

elly's long hair:

a. if the salon only takes cash, then this isn't the problem. it doesn't matter how much she has in her checking account. she can't get a haircut until she has the cash.

b. if she has overdraft protection, then there's no problem. she can go ahead and write a check that her account can't cover, then sometime later, pay the bank some outrageous usury for loaning her a few bucks for a few days, but with beautiful hair.

c. if elly has some principles, and doesn't want to write a bad check, then now she has a problem. her desire for the new hairstyle is in conflict with her honesty and integrity.

d. if the bank will not process a check she writes, then even if she had a million $$ in her account, she couldn't use any of it. the amount she has in her account is not the problem. and if i may suggest, she might as well close her checking account, and put the money where it'll work for her. it's not doing her a bit of good in a checking account, since she can't write any checks.

justin can't pay the full balance:

a. he can't even handle the credit limit he has now. under no circumstances should he ask for a higher limit.

b. he can ask for the grace period to be extended. but that's no solution, the bank will almost certainly refuse anyway, and there are much better options. he knew the rules of his credit card when he started using it.

c. he definitely should pay the interest on the balance, plus as much of the balance as he can cover at the same time.

d. he definitely should pay the minimum otherwise they could shut down his card. he should also pay as much more as he possibly can. he should also remember the awkward situation he's in, stop buying stuff on credit that he can't afford, and avoid adding any more debt.

i'd say that justin's best best option isn't on this list of choices. what he has to do: pay as much as he can at least the minimum payment plus as much more as he can and then avoid adding more debt.

Answer from: Quest

because if the tool that you are using is not balanced it there would be false mass.

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The path of motion of a 8-lb particle in the horizontal plane is described in terms of polar coordin...