An engineer in a locomotive sees a car stuck
on the track at a railroad crossing in front of
the train. when the engineer first sees the
car, the locomotive is 170 m from the crossing
and its speed is 25 m/s.
if the engineer’s reaction time is 0.68 s,
what should be the magnitude of the minimum deceleration to avoid an accident?
answer in units of m/s^2

Explanation:

So we want the speed to go from 25 m/s to 0 m/s in 170 m, but the time  needs to incorporate the reaction time, so the slowing down will not start until .68 s pass.  Or, in other words, the train will travel an extra 25 m/s * .68 s = 17 m.  This means, instead of 170 m to slow down it has 153.  Hopefully that makes sense.  With this information we can use the equation vf^2-vi^2=2ad.  If that equation is unfamiliar you need to get a better handle on your physics equations.

Anyway, let's plug in.  

vf = 0 m/s

vi = 25 m/s

a is what we're trying to find

d = 153 m

vf^2-vi^2=2ad

a = (vf^2-vi^2)/(2d)

Can you handle figuring it out from there?  or if there is something you don't understand let me know.  

Explanation:

As we know that during reaction time the train will move with uniform speed

so here the distance moved by the train is given as

now the distance remaining from the position of the car

now we know that train must stop with in the range of above distance

hi there if you are asking for conformation that wavelingth is the correct answer is wrong it is the answer is frequency. : )

i hope this you out, have a wonderful day

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.