Either the third equation is wrong or I am .

I need help. The question came up in my mind from nowhere. I took u=5 m/s , v=-5m/s and s=10 m. Using the third equation ,I tried to calculate the acceleration which lead to a disaster.

v^2=u^2+2as

-5^2=5^2+2a10

25=25+20a

0=20a

0=a

This is a very surprising result as v is not equal to u. But according to the result, there is no acceleration.

SOS.

#Mechanics #Thirdequation #3rdequation

Easy Math Editor

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Comments

The problem is that s cannot equal 10. If you start at 5m/s and end at -5m/s with a constant acceleration then you are going to go forward a certain distance but then go backwards exactly the same distance so s=0

gordon crawford - 6 years, 8 months ago

A good answer but then what about the acceleration . Will it also be zero?

Platinum Grieger - 6 years, 8 months ago

No, from the u and v values you know a has to be non zero and negative but you cannot know anymore about it from this equation. To find a you would need to use one of the other equations of motion and need some extra information like t.

gordon crawford - 6 years, 8 months ago

@Gordon Crawford – So, I cannot my eyes and use third equation in every case. Thank you.

Platinum Grieger - 6 years, 8 months ago

@Platinum Grieger – Well there is a way to use this equation but you have to split the question up into two parts, if you consider the two directions of motion separately. If you take u =5 v = 0 and s = 5 and then u = 0 v = -5 and s = 5 then you can find the value of a you are looking for.

gordon crawford - 6 years, 8 months ago

@Gordon Crawford – That was awesome

Platinum Grieger - 6 years, 8 months ago

Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$