## Curry one year ago Simple question. But trick involved. A ball is thrown horizontally from the top of a 10 meter high builiding. It strikes the ground at an angle of 30 degree. with what speed was it thrown?

1. Curry

@Miracrown

2. Curry

@ganeshie8

3. ganeshie8

was the angle with respect to ground ?

Is it 20√6m/s

5. anonymous

thrown horizontally means angle was 90 degree |dw:1433846133143:dw| assuming no drag force , so the horizontal velocity is constant call it V0 and the vertical velocity is Vy =zero so the final vertical velocity is $V _{T}^{2}-V_{y}^{2} = 2 g h$ thus you have vy |dw:1433846575866:dw| so $\tan 30 = \frac{ V _{0} }{ V _{y} }\rightarrow V _{0}= V _{y}* \tan30$ just plug in numbers

6. anonymous

uh..oh I mixed Vt with Vy. hope you get the main point

7. Curry

hey, using the equation you gave me, the answer comes out to 8.1. But the actual answer is 24.

8. Curry

What i did was take the time it takes get to the bottom. Then i found out the horizontal distance using trig. Then i divided distance by time. Why is that wrong?

9. Curry

@freckles

10. Curry

@nincompoop @IrishBoy123

@curry, what time did you get for the ball to fall that vertical distance of 10 meters? I got 1.43 seconds.

|dw:1433885146576:dw| @Catch.me

Uh Oh gotta go now, but will return to see how this turned out lol

14. Curry

Yes, i got 1.43 seconds for time also. And then for the horizontal distance i got 10rad3. So i divided this value by 1.43 to get the horizontal speed. But that's not giving me the right answer.

15. Curry

|dw:1433887281746:dw| This is the diagram given. With the curved path being the path of the ball.

16. Curry

Wait I think catch.me is correct actually. The time it takes to get to the bottom is 1.42 seconds. So the Vy is 9.8*1.42. tan(30) = Vy/Vx. Giving us a value of 24 m/s. I understand why this way works. But I still don't understand why the other way doens't work.

17. IrishBoy123

$$10 \sqrt{3}$$?

18. IrishBoy123

@curry medal to @Catch.me would be fair. at time of writing, none.

19. anonymous

@radar yeah i should be 60 @Curry how did you calculate horizontal distance?

|dw:1434062799673:dw| @Curry I used the law of sines. Sin 60/x = Sin 30/10. I'm not sure if that would of given me the horizontal distance, but that is what I used.

21. anonymous

The curve is parabola not straight line( angle is changing) vt= 14 m/s v0= 14 root 3 time = delat v/g=10/7 x= 20 root 3