## carolinar7 one year ago a ball is thrown straight upward with a speed of 20 m/s with what speed does the ball hit the ground?

1. carolinar7

and i have another one the total time of all remains in the air is 14 seconds. a)with what speed was the ball thrown upwards b)what is the maximum height reached by the ball

2. carolinar7

I say 20m/s for the first one

3. carolinar7

|dw:1442888398239:dw|

4. anonymous

at highest point speed=0m/s v=u+gt 0=20-9.8 t t=20/9.8=2s approx time of flight=2*2=4s

5. anonymous

yes you are correct.

6. carolinar7

what is the 0 in 0=20-9.8 t

7. anonymous

speed at highest point.

8. carolinar7

9. carolinar7

ok

10. anonymous

forsecond take t=14/2=7 seconds and proceed as i have done.

11. carolinar7

idk

12. carolinar7

would the acceleration be + or-

13. carolinar7

+ right?

14. anonymous

0=u-9.8*7 u=?

15. anonymous

when going upward g is -ve,when going down g is +ve.

16. carolinar7

why are you using half the time why not the whole 14 seconds?

17. anonymous

|dw:1442899612575:dw|

18. anonymous

|dw:1442899702335:dw|

19. carolinar7

oh so would it be 69 m/s

20. carolinar7

for a)

21. carolinar7

oh and is it + or - accelaration?

22. anonymous

69 m/s approx or68.6m/s

23. carolinar7

why is it - acceleration

24. carolinar7

if its going upwards

25. anonymous

$v^2-u^2=2as$

26. anonymous

because it is retardtion and speed is decreasing.

27. carolinar7

and for be is it 48x10 m

28. carolinar7

?

29. carolinar7

b) 48x10 m?

30. anonymous

$0^2-68.6^2=-2*9.8*h$ $h=\frac{ 68.6*68.6 }{ 2*9.8 }=7*34.3=240.1m$

31. carolinar7

a stone is dropped from 150 meters high .initial velocity is zero. a)with what speed does the stone strike the ground b)how long is the stone in the air c)sketch a position vs time graph for the stone

32. anonymous

$v^2-u^2=2gh$

33. carolinar7

This is what I did $\frac{ 69 m/s +0 m/s}{ 2 }(14 s) =Deltax$

34. carolinar7

for the second question part b