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Direct proportion question

A ball falls vertically after being dropped. The ball falls a distance, d metres, in a time of t seconds.
d is directly proportional to the square of t.



I worked out the first question which was the formula:

d=5t2d=5t^2


Another question was, calculate the time the ball takes to fall 605m

So i did

5t2=d5t^2=d

5t2=6055t^2=605

5t2=1215t^2=121

5t=11s5t=11s

That was the final answer, however i was wondering, do i not divide by 5 to get t on its own?

If not for this one, do i ever? Or do you leave a number next to it always?


Thank you! :smile:
Reply 1
Avatar for TenOfThem
TenOfThem
18
did you not divide by 5 to get from 605 to 121
Reply 2
Avatar for IgorYakov
IgorYakov
OP
3
Original post by TenOfThem
did you not divide by 5 to get from 605 to 121




Aaah right yeh! So it would just be t2=121t^2=121

then Sqrt that? :O?
Reply 3
Avatar for TenOfThem
TenOfThem
18
yup :smile:
Reply 4
Avatar for TenOfThem
TenOfThem
18
Original post by DeathByBSOD
My Maths is kinda rusty, :s

so i think its:

d=5t2d=5t^2

5t2=d5t^2=d

5t2=6055t^2=605

5t=6055t=\sqrt 605

5t=6055t=\sqrt 605
Therefore,
t=605/5t=\sqrt 605/5 ~ 4.92s


This is incorrect ... the OP now has the correct answer
Reply 5
Avatar for IgorYakov
IgorYakov
OP
3
Original post by DeathByBSOD
My Maths is kinda rusty, :s but where did you get the 5 FROM?

so i think its:

d=t2d=t^2

t2=dt^2=d

t2=605t^2=605

t=605t=\sqrt 605


Therefore,

= 24.60s (2d.p)





the 5 is from the first part of the question, when 20 is directly proportion to 4k so k=5
Original post by IgorYakov
the 5 is from the first part of the question, when 20 is directly proportion to 4k so k=5



Ah Ok thanks.

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