Question

.

Answer 1

A stone is thrown vertically upward with an initial speed u from the top of a tower, reaches the ground with a speed 3u. The height of the tower

Answer 2

Try using conservation of mechanical energy

Answer 3

We can use v^2 = u^2 +2as

Answer 4

Yeah sure

Answer 5

@No.name please please post the questions in relevant section :)

Answer 6

how to use , i have a problem considering signs
@vishweshshrimali5 , i knew u would say this , but this was in math

Answer 7

Really ?

Answer 8

Well okay for signs

Answer 9

Consider a reference coordinate system

Answer 10

Like this ^^^

Answer 11

Yes , in dynamics, i will give u a screen shot of that later , i gave ganesh

Answer 12

\(\Large mgh + \frac 12mu^2 = \frac 12m(3u)^2\)

Answer 13

OK

Answer 14

Then your u would be +ve, 3u would be negative, g would be negative

Answer 15

Or you can use the conservation mechanical energy as @aum used :) (I generally use this one as it doesn't uses signs)

Answer 16

Wait
5u^/g ?

Answer 17

?

Answer 18

5u^2/g

Answer 19

Sorry would have to go now :(

Answer 20

oh @Abhisar then is it right

Answer 21

@aum am i correct

Answer 22

u got it @No.name ?

Answer 23

i got the answer as
5u^2/g is it correct

Answer 24

okay..let's see !

Answer 25

Okay

Answer 26

What will be the final velocity when the stone returns at the top of the tower ?

Answer 27

Yes wait that's were the problem is
would it be
(-3u) or -(3u) ?

Answer 28

why - u
It is thrown upwards

Answer 29

Its okay.... now use third equation of motion to find s

Answer 30

By both methods I am getting \(\Large h = \frac{4u^2}{g}\)

Answer 31

and that is correct !

Answer 32

(-3u)^2 = u^2 -2gs

Answer 33

\(\huge\checkmark\)

Answer 34

+2gs

Answer 35

+2gs

Answer 36

yep !

Answer 37

g is negative right?

Answer 38

No, if u take 3u +ve then g must be +ve

Answer 39

if u take g -ve then 3u will also be -ve

Answer 40

I take 3u as negative

Answer 41

If you take the downward direction as positive, then u, 3u, g are all positive.

Answer 42

yes that's what actually happens !

Answer 43

Then u would be negative because the ball is thrown UPwards

Answer 44

It's all on the basis of cartesian coordinates.

Answer 45

Not talking about the upward u but the u when it is traveling downwards

Answer 46

what??