Question

what is the acceleration of a body moving with constant acceleration covers the distance between two points 60m apart in 60sec? its velocity as it passes the second point is 15m/sec

Answer 1

\[ \frac{ \Delta v}{ \Delta t} = a \]

Answer 2

@AllTehMaffs they didn't say it starts at rest, how can you know \(V_0 =0\)?

Answer 3

you're right :( Sorry, I was bein' lazy.

Then solve for u_0 in terms of acceleration and time

\[ \frac{u-u_0}{t} = a
\\ \
\\ u_0 = u - at
\\ \
\\ s = (au-t) + \frac{1}{2}at^2 \]

Answer 4

bah, I'm awful

\[s = (u - at)t + \frac{1}{2}at^2 \]

Answer 5

\[a = 2\frac{s - ut}{t^2}\]

Answer 6

^_^

Answer 7

Does that make sense @jontutz99 ?

Answer 8

@AllTehMaffs what is u_O?

Answer 9

but what formula should i use to get vo?

Answer 10

The one you would normally use to find a constant acceleration

\[ a=\frac{\Delta v}{t} = \frac{v-v_0}{t}\]
\[ at = v - v_o\]
\[v_0 = v - at\]
we solve for it in terms of the velocity and time that we know ^^

Answer 11

Then we can put that into the normal displacement equation
\[ s = v_0t + \frac{1}{2}at^2 \]
\[s = (v - at)t + \frac{1}{2}at^2\]

Answer 12

ohh i get sir thanks :)

Answer 13

Very welcome ^_^

Answer 14

@AllTehMaffs sir you still online? i got a problem i get a - acceleration..

Answer 15

That's okay. That just means it's slowing down ^_^

Answer 16

sir should i use the formula s=(v−at)t+1/2at^2 to get the accel? or the other formula of a?

Answer 17

cause i got a high Vo i got a 29.5 vo x.x i think im doing it wrong sorry

Answer 18

hmm. That is fast1 ^_^ what did you get for a?

Answer 19

And don't worry - getting things wrong is half the fun! ^^

Answer 20

uhh.. if i use the s formula i get 0.466666666 if i use the a formula i get -0.466666666

Answer 21

which means I made a mistake somewhere. I sec.. :P

Answer 22

oh ok sir

Answer 23

the acceleration formula is wrong, sorry about that. I messed up a sign. The top should be (vt - s).

The acceleration then turns out to be positive, and the initial velocity is negative.

darn +'s and -'s :P ^^

Answer 24

Good intuition that the initial velocity was too big ^_^ I'm impressed!

Answer 25

@AllTehMaffs i think we still got problem sir xD i got a high initial velocity .. the answer i got from the formula was 12.999999999 and the answer must be 1.67 so far x.x

Answer 26

The correct answer is 1.67?

Answer 27

yah 1.67 m/sec

Answer 28

For the initial velocity?

Answer 29

ahh nope for the acceleration oh sorry the answer i get for acceleration is 0.466666666 and the answer was suppose to be 1.67 sorry for that

Answer 30

I'm really sorry that I've messed this up so many times for you :/ 1 sec...

Answer 31

haha thats ok. important is you helping me :)

Answer 32

And you're sure the time and displacement are
t= 60s
d = 60 m
?

Answer 33

yah.. that was the given

Answer 34

I have absolutely no idea how to get 5/3 as an answer. I'm sorry. There is some fundamental thing either missing in the problem or in my brain. If you use those numbers and just outright solve for v_o

\[ d = \frac{v+v_0}{2}t\]
\[ 2d/t = v+v_0\]
\[2m/s - 15m/s = v_0 = -13m/s\]

and that's what you get from the acceleration equation too. So it's not a miscalculation with any individual part of my setup. I have no idea. I think your answer is wrong. Or I'm crazy.

Answer 35

xDD nvm sir thanks again for the help.. maybe ill try it nxt tme btw sir got any knowledge about parallel force?

Answer 36

what's the problem? I'll try my best ^_^

Answer 37

if a force of 86 N to the surface of 20 degree inclined plane will push a 120-N block up the plane at constant speed. what force parallel to the plane will push it down at constant speed?

Answer 38

Can you draw a force diagram?

Answer 39

uh.. sorry sir no fig here x.x

Answer 40

So the first force is pushing completely horizontal?

Answer 41

yes

Answer 42

oh btw the answer here is 45 N

Answer 43

My brain is not understanding what to do. I'm very, truly sorry. I need to sleep on it - can I get back to you tomorrow?

Answer 44

yah sure ok thanks :)

Answer 45

I apologize for my complete uselessness. G'night, and I'll try again tomorrow ^_^

Answer 46

thats ok haha