Physics, 14.04.2020 16:07 Mads4865

A disk, with a radius of 0.25 m, is to be rotated like a merry-go-round through 800 rad, starting from rest, gaining angular speed at the constant rate through the first 400 rad and then losing angular speed at the constant rate - until it is again at rest. The magnitude of the centripetal acceleration of any portion of the disk is not to exceed 100 m/s2. (a) What is the least time required for the rotation

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Answer from: joree

a) $T_{min} = 80\,s$

Explanation:

a) Let consider that disk accelerates and decelerates at constant rate. The expression for angular acceleration and deceleration are, respectively:

Acceleration

$\alpha_{1} = \frac{\omega_{max}^{2}}{2\cdot (400\,rad)}$

Deceleration

$\alpha_{2} = -\frac{\omega_{max}^{2}}{2\cdot (400\,rad)}$

Since angular acceleration and deceleration have same magnitude but opposite sign. Let is find the maximum allowed angular speed from maximum allowed centripetal acceleration:

$a_{r,max} = \omega_{max}^{2}\cdot r$

$\omega_{max} = \sqrt{\frac{a_{r,max}}{r} }$

$\omega_{max} = \sqrt{\frac{100\,\frac{m}{s^{2}} }{0.25\,m} }$

$\omega_{max} = 20\,\frac{rad}{s}$

Maximum magnitude of acceleration/deceleration is:

$\alpha = 0.5\,\frac{rad}{s^{2}}$

The least time require for rotation is:

$T_{min} = 2\cdot \left(\frac{20\,\frac{rad}{s} }{0.5\,\frac{rad}{s^{2}} } \right)$

$T_{min} = 80\,s$

Answer from: Quest

the answer is b

explanation:

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.

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A disk, with a radius of 0.25 m, is to be rotated like a merry-go-round through 800 rad, starting fr...