Maximum displacement? Maximum velocity? (SHM) (1 Viewer)

[goobi]

In Q.18 in Ex. 6.10 from Maths in Focus,
"A weight is oscillating at the end of a spring, with velocity given by . Find the maximum velocity of the weight."
My solutions are:

When ,


The answer provided by the author is just 30cm/s, but I think it is imperative to include both +30cm/s and -30cm/s as the answers because the signs indicate nothing but the directions of the velocity of the particle.

Moreover, in the same exercise, Q.9 reads, "A particle's displacement is given by at time t seconds. Find the maximum displacement."

However, the answers to this question provided by the author are which are sort of contradictory to the answer to Q.18 as mentioned above.

So I wonder if I need to include both the positive and negative solutions when answering this kind of question.

Thanks in advance for any help

 

[Carrotsticks]

For the first one, we just want the magnitude so 30cm/s will suffice.

For the second one, I would have put 2 as will as the maximum displacement.

It's really up to you but if you were to receive this in an exam, at least somehow let your examiner know that you have considered plus/minus etc.

But I do understand the frustration regarding how there is a bit of ambiguity with this.

 

[Peeik]

Yeah i reckon the signs are important because both velocity and displacement are vector quantities which need both a magnitude and direction. Had the question asked for speed, then you neednt bother with the signs.

 

[goobi]

For the first one, we just want the magnitude so 30cm/s will suffice.

I wonder why we just want the magnitude... The question is asking for the ''velocity'' which is a vector defined by both magnitude and direction... So, if we only take the magnitude as the solution, we are just finding the speed but not the velocity which is the question asking for.

For the second one, I would have put 2 as will as the maximum displacement.

What do you mean?

 

[goobi]

Yeah i reckon the signs are important because both velocity and displacement are vector quantities which need both a magnitude and direction. Had the question asked for speed, then you neednt bother with the signs.

This.