## mcd173 3 years ago A skier (m=57.0 kg) starts sliding down from the top of a ski jump with negligible friction and takes off horizontally. If h = 6.20 m and D = 13.4 m, find H.

1. chand

what is "h" ?

2. chand

Use the energy method. Decrease in potential energy= gain in kinetic energy mg(H-h) = 1/2 mv^2 here we get the velocity. After taking off, the range is given by R= u. t where "t" is the time of descent and 'u' is the velocity.

3. chand

Hope its clear

4. hosein

(1/2)mv^2=mgD so v=sqrt(2gD) v on above is v0 for next part of ask (when skier leave ski jump) y=(v0^2/2*g) so H=y+h

5. chand

isn't "d" the distance covered after he jumped?

6. hosein

i think D is ski jump's length

7. hosein

i drew above do you solve it?

8. chand

D should be the range i feel.

9. chand

Let us take D to be the range. Now, decrease in potential energy would be mg(H-h) as he came down a height of H-h So, mg(H-h) = 1/2 mv^2 v=(2g(H-h))^1/2

10. hosein

question want H did you get it?

11. chand

yes.

12. hosein

so it is...?

13. chand

approximately 15.026

14. hosein

how did you get time of descent

15. chand

t= {2h/g}^1/2

16. hosein

this t is time of H time of descent is: 2*t

17. hosein

how did you take v=u in two formula? mg(H-h) = 1/2 mv^2 R= u. t

18. chand

D= v. t where v= [2g(H-h)]^1/2 and t= [2h/g]^1/2 "t' is the time of descent from "h" to the ground. I typed u instead of v

19. hosein

u is velocity of body when it's arrive to ground but vis velocity in top of path

20. hosein

no i think you use 2*t in formula for D

21. hosein

hence d is all of horizontally path

22. chand

|dw:1331643793186:dw|

23. chand

"v' is the velocity of the man before taking off. We are not concerned about the velocity which he will have while landing on the ground

24. chand

Yes "D" is the horizontal distance covered.

25. hosein

did you see my diagram ? H is max height that man arrive . i didn't understand your fig

26. hosein

i mean that how did you yeild to u=v

27. chand

When a body takes off horizontally, the height from which it took off will be the maximum height. i took that the person slides from a height "H" and after reaching a height "h', he takes off and covers a horizontal distance 'D". I mistyped u or v.

28. chand

mistyped u for v

29. chand

am i clear?

30. hosein

yes you'r right