Question

a stone is dropped in to a well 20 deep.another stone is dropped 1 seconds later..if both reach the water surface simultaneously ,v is equal to?

Answer 1

take g = 10 ms^-2

Answer 2

Optiona:
30
15
20
10

Answer 3

Ah i assume you are saying the first is thrown with some initial velocity.

Answer 4

I have typed the entire question.

Answer 5

dropped usually means they have the same initial velocity of 0 so unless you are figuring in air drag, The second should hit the water 1 second later than the first.

Answer 6

nothing is mentioned...so u = 0?

Answer 7

But based on your question I would have to assume one has an initial velocity that isn't zero so that they can both hit at the same time.

Answer 8

yea thats correct

Answer 9

if initial velocity is zero for both stones they will not hit the water at the same time.

Answer 10

So in that case I would assume the second is perhaps dropped and the first is thrown up, or alternatively the first is dropped and the second is thrown down.

Answer 11

if we apply the formula v^2 = u^2 + 2as
v^2 = 0^2 + 2*10*20
v = sqrt400

Answer 12

v = 20ms^-1 then...but thats incorrect...

Answer 13

Sure you could go that way, hes not done, he just saying that the stone dropped with an initial velocity of 0 will have a final speed of 20, and using vf=vi+at you could solve that it occurs in 2 seconds.

Answer 14

well thats is correct for a stone dropped with zero initial velocity

Answer 15

but here we have take initial v as u right?

Answer 16

So then you could solve for vi for a stone that drops 20 in 1 seconds or 3 seconds depending on the setup of the problem.

Answer 17

or u as you call it

Answer 18

lets see if you use t=1 you would have 20=v*1+1/2*10*1^2, which yields 20=v+5 so if they throw it down at 15m/s, the second would catch up

Answer 19

the question as it stands does not make sense. The second stone must have u>0 for them to arrive at bottom at same time.

Answer 20

or alternatively if t=3 you would have 20=v*3+1/2*10*3^2. 20=3v+45 -25=3v or v=25/3 thrown up, but ultimately welshfella is correct, really need the original problem as this one doesn't make sense.

Answer 21

Though from your options I would lean towards the 15.

Answer 22

lemme redo it
s = ut + 0.5st^2
20 = u + 0.5*10*1
20 = u + 5
u = 15?

Answer 23

That would be if we are looking at the case where the first is dropped and the second is thrown down, and the second s in the first line would be an a.