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Member advised to use the homework template for posts in the homework sections of PF.

Actually that's very easy question but I have some difficult to understand the logic behind .

So-"The initial velocity of an object (m/s) is Vi=1i+5j+2k. And the final velocity is Vf=3i+5j+7k. What was the change in speed of the object?"X

Solution -

|Vf|-|Vi| = √(3

My question -

If I would do |Vf-Vi| - why is it wrong ? And what is the meaning of the scalar I get from this equation? Has to be some connection to the "change in speed". I just can't see it clearly.

Thanks again, just started to learn physics and I love it.

So-"The initial velocity of an object (m/s) is Vi=1i+5j+2k. And the final velocity is Vf=3i+5j+7k. What was the change in speed of the object?"X

Solution -

|Vf|-|Vi| = √(3

^{2}+5^{2}+7^{2})-√(1^{2}+5^{2}+2^{2}) = 3.63 m/sMy question -

If I would do |Vf-Vi| - why is it wrong ? And what is the meaning of the scalar I get from this equation? Has to be some connection to the "change in speed". I just can't see it clearly.

Thanks again, just started to learn physics and I love it.