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Easy Physics Problem...

I

ipodtouchy333

macrumors 65816
Original poster
Nov 15, 2007
1,055
0
US
A rocket-driven sled running on a straight,
level track has been used to study the physio-
logical effects of large accelerations on astro-
nauts. One such sled can attain a speed of
395 m/s in 1.6 s starting from rest.
What is the acceleration of the sled, assum-
ing it is constant?

We are starting the chapter tomorrow and I'm not quite sure how to get the final answer. Anyone? Thank you.
 
solution

395m/s (want m/s^2)

so divide by 1.6s to achieve that velocity

395/1.6 = 246.875
 
wakwe said:
.. a=dx/dt^2?
Click to expand...

I was giving the benefit of the doubt to the OP... if the OP can already do calculus, I'd be really shocked that he/she couldn't solve this problem on his/her own. :p

But it's always good to understand the general principle underlying the answer, so that the other three million problems that are exactly the same as this one can be solved in the same way, and in a month or two, when this problem is embedded as just a part of a much larger problem, that part will seem intuitive once one gets there. :)
 
Oh duh! Jeeze thanks guys! Ok one more question...

An electron, starting from rest and moving
with a constant acceleration, travels 4.6 cm in
8.2 ms.
What is the magnitude of this acceleration
in km/s 2 ?

Sorry about this, it just really annoys me when our teacher assigns us homework when we haven't a clue what we're doing yet...
 
ipodtouchy333 said:
Oh duh! Jeeze thanks guys! Ok one more question...

An electron, starting from rest and moving
with a constant acceleration, travels 4.6 cm in
8.2 ms.
What is the magnitude of this acceleration
in km/s 2 ?

Sorry about this, it just really annoys me when our teacher assigns us homework when we haven't a clue what we're doing yet...
Click to expand...

See, that's the point. You solve this with exactly the same equation wakwe posted above. x is the distance, a is the acceleration (well, assuming this is a non-relativistic problem, but again, if you're asking the question, I'm sure it is :p ). In this case, there's no initial acceleration:

x = v0 * t + 1/2 * a0 *t^2 + x0

V0 is zero. X0 is zero. Plug in X and the time and solve for a0.

If you keep approaching each problem like it's completely unrelated to the one before it, then physics is a disaster... if you approach from general principles it becomes beautiful.
 
Yeaaaa...still can't get it. Maybe I shouldn't have taken AP Physics but thanks for everyone's help anyways!
 
I did try it, yes. I probably sound like the dumbest person ever right now but when I converted to km/s I came out with a reallllyy small number and I just don't think that's right.
 
Convert the original values to the desired values (cm to KM and ms to s) and plug into the above formula!
 
GOT IT! I forgot to square the t in the equation...wow. Thanks everyone and sorry I sounded like such a dummy, haha.
 
395 m/s in 1.6 seconds
395 = 3 sig fig
1.6 = 2 sig fig
so answer must be two sig fig

∴ 395/1.6 = 246.875 m/s/s (m/s^2 OR ms^-2)

∴ Acceleration ≈ 250 m/s/s (2 sig fig)
 
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