# Kinematics question help?Watch

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#1
A little stuck on how to answer these questions:

-On the position time graph, for which part of the 10 second time period does the object have a negative velocity and a positive acceleration?

-On the position time graph, for which part of the 10 second time period does the object have a negative velocity and a negative acceleration?

-On the position time graph, for which part of the 10 second time period does the object have a positive velocity and a negative acceleration?

For each the answers must be between 0-2, 2-4, 4-6, 6-8 or 8-10.

I understand that the gradient of the graph corresponds to the velocity and the gradient of the velocity corresponds to acceleration etc, however it won't accept any of my answers!
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2 years ago
#2
(Original post by YeoniSmol)
A little stuck on how to answer these questions:

-On the position time graph, for which part of the 10 second time period does the object have a negative velocity and a positive acceleration?

-On the position time graph, for which part of the 10 second time period does the object have a negative velocity and a negative acceleration?

-On the position time graph, for which part of the 10 second time period does the object have a positive velocity and a negative acceleration?

For each the answers must be between 0-2, 2-4, 4-6, 6-8 or 8-10.

I understand that the gradient of the graph corresponds to the velocity and the gradient of the velocity corresponds to acceleration etc, however it won't accept any of my answers!
sounds like you understand... the gradient of the line is
Δy/Δx
straight line sections of the distance time graph mean constant velocity - the gradient of the line at any point is the value of the velocity at that point (can be +ve, -ve or 0)

so if the gradient is always positive over a period of time then the velocity is positive over that period of time and vice versa.

now if the gradient of the line shows change over time this means non constant velocity (i.e. acceleration). If the gradient is becoming more +ve over a period, then it's a positive acceleration and if it's becoming more negative over a period then it's a negative acceleration (or deceleration)

might help if you drew up a table of the time periods 0-2, 2-4, 4-6, 6-8, 8-10 with a couple of columns - first column for the gradient of the line showing whether it's +ve 0 or -ve over the period
second column showing whether the gradient had a +ve 0 or -ve change over the period.
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