## mayankdevnani 3 years ago A body of mass 2 kg is thrown up vertically with a kinetic energy of 490 J.If the acceleration due to gravity is 9.8 m/s^2, the height at which the kinetic energy of the body becomes half of the original value is - a) 50 m b) 25 m c) 12.5 m d) 10 m

1. mayankdevnani

@Hero @hartnn @Chlorophyll @robtobey @sauravshakya @kropot72 @jiteshmeghwal9 @hba

2. mayankdevnani

@mathslover have a look:)

3. mathslover

First find the original value ... what you get?

4. mayankdevnani

original value????

5. mathslover

sorry i think it is given

6. sauravshakya

Potential energy of the body =mgh

7. sauravshakya

u know it?

8. mayankdevnani

ok!!

9. mayankdevnani

yaa

10. mathslover

490 J = KE (ORIGINAL)

11. mayankdevnani

yaa

12. mathslover

half of it will be 490 /2 J = 245 J , correct?

13. mayankdevnani

why you do the half the K.E @mathslover

14. mathslover

@mayankdevnani because we have to find the height when the new kinetic energy equals half of the original one. ...

15. mayankdevnani

@03225186213

16. mathslover

therefore the new kinetic energy must be equal to 245 Joules.

17. mayankdevnani

yaa

18. mayankdevnani

correct!!!

19. mathslover

therefore we have : 1/2 m v^2 = 245 J 1/2 m (u^2 + 2gh ) = 245 J 1/2 m (2gh) = 245 mgh = 245 J 2 kg * 9.8 * h = 245

20. mathslover

solve for h and you will get h = 12.5 m

21. mayankdevnani

1/2 m (u^2 + 2gh ) = 245 J ??????????????

22. mathslover

got it?

23. mayankdevnani

no!!!!

24. mayankdevnani

1/2 m (u^2 + 2gh ) = 245 J this line!!!

25. mathslover

since v^2 = u^2 + 2gh therefore..

26. mayankdevnani

ok

27. mayankdevnani

thnx.... i got it @mathslover

28. mathslover

good,...

29. mayankdevnani

let @03225186213 be answer.... plz wait

30. 03225186213

1/2 mv^2=mgh 490/2=2 (-9.8)h h= -9.8 because it is moving against gravity

31. mathslover

@03225186213 same I thought BUT it is given in the quest. that g = 9.8 m/s^2

32. mayankdevnani

yaaa you are correct thnx @mathslover and @03225186213

33. 03225186213

welcome

34. mayankdevnani

:)