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Speed = d/t formula

Just wondering why the s=d/t formula can't be used for part 2 of this question ?

The time in the first part was 4.16

I got the time, and speed, do distance= 5*4.16 = 20.8 , I know I could use suvat but not sure why this method couldn't be used as I get it wrong.
(edited 11 years ago)
Original post by Tulian
Just wondering why the s=d/t formula can't be used for part 2 of this question ?

The time in the first part was 4.16

I got the time, and speed, do distance= 5*4.16 = 20.8 , I know I could use suvat but not sure why this method couldn't be used as I get it wrong.


s=d/t is for when you have constant speed (or average speed).

In this situation you have the speed at the start of the motion, but it's changing as the object is decelerating.
Reply 2
Avatar for Vulpes
Vulpes
15
Original post by Tulian
Just wondering why the s=d/t formula can't be used for part 2 of this question ?

The time in the first part was 4.16

I got the time, and speed, do distance= 5*4.16 = 20.8 , I know I could use suvat but not sure why this method couldn't be used as I get it wrong.


s = d/t can only be used for objects travelling at a constant speed. The block B in this case is decelerating.

Use s = ut + 0.5 at^2 where:

s = ?
u = 5
a = -1.2
t = 4.17

(before anyone points it out, im just too lazy to type in the units above)
Reply 3
Avatar for Tulian
Tulian
OP
Thanks alot :smile:
Reply 4
Avatar for najinaji
najinaji
18
Original post by Tulian
x

Was too late to help out, but I just wanted to wish you luck for your exam. :smile:

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