Very Simple A nice prob

Consider a elevator accelerating upward with 2.4m/s2.
Inside the elevator there is a ball of mass 1kg tied to the ceiling using a massless string.
The elevator travels 30m up and then the string breaks and the ball is let loose.

Calculate the time taken by it to reach the floor of the elevator which is 5m away from the hanging ball.

13 Answers

62
Lokesh Verma ·

1/2 g. t2 = 2.4

t2 = 4.8g

v= √4.8 t

downward, displacemnt will be 35 m for the ball..

-35= √4.8 tt - 1/2 g t2

now solve for t

there iwll be one -ve root. ignore that :)

11
virang1 Jhaveri ·

Bhaiyya the displacement is not 2.4 it is 30m of the elevator with the ball intact to the ceiling. 2.4 is the acceleration of the elevator and after 30 m the string holding the ball breaks and the ball falls . The time according to me is 0.67seconds

Please tell me if i am wrong

3
iitimcomin ·

lets luk at i frm outside point of view ..........

2(2.4)30 = v =initial vel. upwards ..........

1/2gt2 - vt = 5 - distance covered by base of elevater in dat time.......

11
virang1 Jhaveri ·

No iitimcoming it is wrong pls read the question again

11
virang1 Jhaveri ·

You forgot that when the string breaks the ball has a upward velocity which has to be considered.

3
iitimcomin ·

ive concidered it ,,, luk at mah soln.

11
virang1 Jhaveri ·

I think that you have not considered the acceleration of the elevator and its velocity.

3
iitimcomin ·

""""""""""""lets luk at i frm outside point of view """""""""

is a key statement ... so i havnt included psudo force bhai.....

u can do it other way also...

3
iitimcomin ·

""""""distance covered by base of elevater in dat time"""""""""""

covers all that ....

11
virang1 Jhaveri ·

ok i got it I did not read "distance covered by the base of the elevator"

You r rite.

11
mona100 ·

wats the correct answer???????

i am getting 1.15 sec.

11
virang1 Jhaveri ·

Yes Mona your answer is rite.

21
tapanmast Vora ·

can sum1 cont. n complete the solutn by IITijmcumin...

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