/sci/ - Science & Math

[Anonymous No.7548626]

Hey I'm really stuck on these two physics questions, please Help!?
A car accelerates from 13.2 m/s to 19.1 m/s in 5.2 s. How many metres did it travel in this time - assuming constant acceleration?

A train of mass 55,200 kg is travelling along a straight track at 24.4 m/s. Suddenly the engineer sees a truck stalled on the track 300.3 m ahead. The maximum possible braking acceleration of the train is 1.68 m/s2. After the brakes are applied, how far short of the truck does the train stop (in meters)?

[Anonymous No.7548646]

4206661488 meters

[Anonymous No.7548659]

>>7548626
>Suddenly the engineer sees a truck stalled on the track 300.3 m ahead.
He ought to become a fighter pilot with eyesight that good

[Anonymous No.7548666]

>>7548626
>highschool level problems
Underage b&

[Anonymous No.7548671]

>>7548626
s=s0+vt+(1/2)a(t^2)
v=v0+at

that's all you need

[Anonymous No.7548695]

>>7548626
Is it a Volkswagen?

[Anonymous No.7548750]

>>7548626

For the first one, d = .5(vi + vf)t.

Substitute in your numbers.
vi = 13.2 m/s
vf = 19.1 m/s
t = 5.2 s
Now you have d = .5(13.2 + 19.1)(5.2)

d = 84 m

---

For the second one, you need to think about it a little bit.

The 55200 kg doesn't actually matter because we already have the acceleration (we don't need to calculate from force); it's there to distract you. The 300.3 m isn't needed until you have the distance it travels.

We know the initial velocity is 24.4 m/s, and the final velocity is 0 m/s because it is stopped. The braking acceleration it gives, 1.68 m/s/s, is opposite the direction of motion. Since we're calling the 24.4 m/s positive, it needs to be -1.68 m/s/s (otherwise, the velocity would not be decelerated to 0).

Now, we can find the time it takes the train to stop.

vf = vi + at
(therefore, t = (vf - vi)/a)

now that we have time, we can find the distance it travels in that time

d = .5(vi + vf)t
and we said t = (vf - vi)/a
so d = .5(vi + vf)(vf - vi)/a

substitute in your values

I get 171 m for the distance

now, you can subtract it from the 300.3 m, and the train stops 129 m short of the stalled truck.

[Anonymous No.7548764]

>>7548750
>spoonfeeding a simple physics question
he'll never get how to manipulate a couple of simple general equations into equations that he can use to solve the given problem that way
copy and pasting answers from someone who already derived the proper equations skips like 95% of the actual work

[Anonymous No.7548776]

>>7548764
I once had trouble with this, too. I don't mind posting it online and trying to be helpful rather than jumping between threads to judge other people. I can't know whether it will be read or merely copied, but it's not my decision to make.

I appreciate your concern for the standards of education, and I believe it is absolutely necessary to learn to solve problems and manipulate equations and relationships. I'd rather make an attempt to be helpful and show that these problems can be broken down and analyzed, however, than ignore someone who is confused. Everyone needs to start somewhere, and failing to arrive at a reasonable conclusion is definitely discouraging. :)

[Anonymous No.7549490]

>>7548764
Is that you?

[Anonymous No.7550176]

>>7549490
>missing the point this badly