Physics, asked by rajendraprasad14, 1 year ago

A stone A is thrown vertically upward with speed U and another stone B is thrown vertically downward with same speed you from a height h the time taken by stone A and B to reach the ground at 16 second and 4 seconds respectively the time taken by another stone to reach the ground after it has been dropped from height H is

Answers

Answered by astha1209

Given, time taken by stone A is 16s

Initial speed = u

Time taken by stone B is 4s

Initial speed = u

final velocity = 0

V = u+at

0 = u+ 10*40

Therefore u for second stone is -40m/s

As the height is same for both the stones,

S = u*16+1/2*-10*16*16 for stone 1 ----(1)

S = -40*4+1/2*10*4*4 ----- (2)

Now, equating eqn. 1 and 2

u*16+1/2*-10*16*16 = -40*4+1/2*10*4*4

u = 75m/s for stone 2

Now, s = 75*16+1/2*-10*16*16

S = -80m

Now for stone 3,

v = 0,

v^2 - u^2 = 2as

0 - u^2 = 2*10*-80

Therefore u = 400m/s

Now, v = u+at

0 = 400+10*t

Therefore time taken by third stone is 40s.

Ayush0605: I can say that your concepts of physics are not clear

Ayush0605: Have you given ANTHE

satishkumar25272: Why not you give the answer bro

Shaanrai17: We will be using the formulae,

Shaanrai17: We will be using the formulae, v = u + at and s = ut + 1/2 * a * t^2. The path of the ball thrown up can be divided into three phases, the going up of the ball (Ball A) from the beginning height to the maximum height (Ph1), then the coming down from max height to beginning height (Ph2), and finally, the going down from beginning height to the surface (earth). Now, as per property, under gravity time taken for Ph1 = time taken for Ph2.

Shaanrai17: The time taken for Ph3 is same as the time taken for Ball B to land, i.e, equal to 4 seconds. So, time for (Ph1 + Ph2) = 16-4 = 12 seconds, and so, time taken for going up or down is 12/2 = 6 seconds.
Now, in Ph1,
V = u + at
0 = u -10 * 6
u = 60
Next, as u is same for both balls,
s = ut + 1/2 * a * t^2
s = 60 * 4 + ½ * 10 * 16
s = 240 + 80 = 320
Finally for the free fall ball,
S = ½*g*t^2
320 = ½ * 10 * t^2
t^2 = 64
t = 8 seconds.
Please comment if anything is not clear. I will try to answer ASAP.

Shaanrai17: Velocity in Ph2 (VR) is equal to, at height h, will be u.
VR = 0 + 10*6 = 60
So, VR = u.

joinpawankumar99: Why you subtract 16 and 4s

Ayush0605: your concepts are not clear

Ayush0605: ans is 8 seconds

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