Kinematics help a level

OP

You can't do this in the exam - it really isn't a good approach.

I see. I mean conceptually I understand what to do. @mqb2766 was explaining why and I know why now.
I think the lack of understanding was the fact that I thought that the boat stops moving completely after 25s but that’s not the case and it still moves just in their other direction.
I think it’s because I’m used to questions when it stops moving.
I’m putting your answer in my notes.

Reply 21

KallamSamad

OP

8

Always check when something is decelerating whenit comes to rest. If that time is within the time periodyou are looking at then this will happen - itdecelerates then stops then moves backwards. The part (a) answer is negative ie it has gonebackwards so you need to check how far forward itgoes for overall distance. Displacement is a vectorbut distance gone is a scalar.
Another thing is I pictured it as an actual boat but it’s not is it? It’s a particle so it doesn’t have to turn etc
Got you
Wow I’ve overcomplicated this

Reply 22

mqb2766

21

Original post by KallamSamad

Always check when something is decelerating whenit comes to rest. If that time is within the time periodyou are looking at then this will happen - itdecelerates then stops then moves backwards. The part (a) answer is negative ie it has gonebackwards so you need to check how far forward itgoes for overall distance. Displacement is a vectorbut distance gone is a scalar.
Another thing is I pictured it as an actual boat but it’s not is it? It’s a particle so it doesn’t have to turn etc
Got you
Wow I’ve overcomplicated this

Theres also the old physics joke of my partner says they love me to the moon and back. I hope they mean distance travelled rather than displacement.

Note Id probably just say you need to be careful when youre asked for the distance travelled, especially when the initial velocity and acceleration have different signs. Simiarly a sketch of both the problem and a typical trajectory with stuff marked on helps.

(edited 1 month ago)

Kinematics help a level

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