## King 3 years ago A baseball player hits a homerun, and the ball lands in the left field seats, which is 120 m away from the point at which the ball was hit. The ball lands with a velocity of 20 m/s at an angle of 30 degrees below horizontal. Ignoring air resistance (A) find the initial velocity and the angle above horizontal with which the ball leaves the bat; (B) find the height of the ball relatively to the ground

1. Mani_Jha

If there is no air resistance, the parabolic path will be symmetrical, and thus it will land at the same velocity with which it left. So $u=20 m/s and \theta=30$ The height will be $h=u ^{2}\sin ^{2}\theta/2g$

2. salini

it is like that concept in which when u fire a bullet vertically up,it comes down same straight line to hit u with same speed with which it went if not for air drag

3. salini

there is a common principle that when a body is thrown up from a certain height,then when it comes back to the same height, it will have the same velocity

4. salini

|dw:1328876734968:dw||dw:1328876550335:dw| sincew the magnitude of velocity is same however when u see the angle made with the horizontal,first it is theta and next it is 189-theta

5. salini

sorry 180-theta*

6. King

ya so ?

7. salini

wat is your doubt in this?

8. King

i dont understand wat is the answer and hw u got it?....i only understood the same velocity thing

9. King

and also in the website there are numerical answers but we didn't get any?

10. King

and can u pls xplain with numerics b'cuz i hate variables in physics and dont understand it

11. salini

|dw:1328877186942:dw| is the question like this or are the bat and ball at the same level?

12. King

no its a parabola same height

13. King

|dw:1328877374070:dw|

14. salini

ok now first draw the diagram with all velocities, distance marked in it with wat u understood

15. King

|dw:1328877495107:dw|

16. salini

in A portion,they ask for angle made with horizontal which is 30 as i explained and the magnitude of velocity is same 20m/s dont bother about the direction being different as when we say that a vector has magnitude and direction, we mean to say that we can write it in terms of i^ j^ k^ anyway my magnitude of velocity remains the same if u want to write that velocity in terms of components i can teach u how to do it the u get a solid vector notation of the velocity when ball leaves bat

17. King

ok...can u teach me hw to write in terms of components?

18. salini

|dw:1328877872806:dw| give me the values for vx and vy

19. King

vy=2cos30 or 20cos30?

20. King

salini?

21. salini

value

22. King

is it 2cos30 or 20cos30 i cant understand..if u tell me that i will calculate the value

23. salini

20*root3/2 and 20*1/2

24. King

i meant it looked like 2cos30

25. King

it is 10sqrt3 and 10

26. salini

|dw:1328878380008:dw|where i and j are direction along x and y axis and are mutually perpendicular to one another

27. King

do u hav to use i cap and j cap?

28. salini

AND THATS HOW U REPRESENT ANY VECTOR YES U HAVE TO TO SPECIFY DIRECTIONS

29. King

hey why u gettin angry?i am not ud at those and we hav to find only magnitude anyways..if u are irritated and dont wanna explain its fine

30. King

*gud

31. salini

no I turned the capslock when i answered arvind

32. King

oh!sry!

33. King

sry salini i shall try frm here on my own...rite nw i gtg!