6r question....

[Omyss]

for those who have taken 6r and still have the test can you clarify the question for me?

#28. The solutions say: Use Big Five #2, and call down the positive direction. Then v0 = –v (it’s negative, because v0 is upward and we’re
calling down the positive direction) and vfinal = +v, so vfinal = v0 + at becomes v = (–v) + gt, or 2v = gt, which gives t = 2v/g.
This means that t is inversely proportional to g. So, if g is decreased by a factor of 6, then t will increase by a factor of 6.

but how can you know that the initial velocity = - final velocty?

I used one of the other big 5 eq'ns:
d = VfT - 1/2at^2
thus since vf is zero t= square root of 2d/a
which gives me the anser that t would increease by a factor of root 6.

Why is this wrong?

---

Members don't see this ad.

 

[MahSpoon]

the equation is X=ViT + 1/2at^2 (initial velocity) not final

I've never used a form with Vf and i substitute in -g as needed

The easiest way to approach this is to use
Vf = Vi -gT
When Vf is zero gT=Vi. Thus, if you have the same Vi and decrease g by 6, you must increase T by 6 to balance the equation. Hope this helps!

 

[Omyss]

there are two equations that look similar but are slightly different.. and their both part of the big five:

d = VoT +1/2aT^2
and
d= VfT - 1/2aT^2 so why didn't this equation work.. thats weird.

 

[IckeyShuffle]

im right there with ya bud. I put the exact same answer as you.

 

[DiverDoc]

there are two equations that look similar but are slightly different.. and their both part of the big five:

d = VoT +1/2aT^2
and
d= VfT - 1/2aT^2 so why didn't this equation work.. thats weird.

this is the equation you use. If i remember right, the answer is 50 meters or point B. Make sure you solve for T. Then use distance equals rate (given) multiplied by time.

 

[Omyss]

this is the equation you use. If i remember right, the answer is 50 meters or point B. Make sure you solve for T. Then use distance equals rate (given) multiplied by time.

your're thinking of the wrong question lol... this one is asking by what factor the time changes...

 

[xylem29]

your're thinking of the wrong question lol... this one is asking by what factor the time changes...

use big 5 # 4 - d= v(initial)t + 1/2gt(sq)

to go up and come back down gives your displacement as zero. then just solve for t.