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QLDPhysicsQuick questions
Unit 2: Linear motion and waves
Quick questions on Motion graphs: position, velocity and acceleration vs time (QCE Physics Unit 2)
7short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is position-time?Show answer
- Slope at a point = instantaneous velocity. - Horizontal line = stationary object. - Straight sloping line = constant velocity.
What is velocity-time?Show answer
- Slope at a point = instantaneous acceleration. - Horizontal line = constant velocity. - Straight sloping line = constant acceleration.
What is acceleration-time?Show answer
- Horizontal line = constant acceleration. - Area under the graph = change in velocity, $\Delta v$.
What is reading $x$-$t$ slope as displacement?Show answer
$x$-$t$ slope is velocity, not displacement. Displacement is read directly off the vertical axis or as the change in $x$.
What is treating area on $x$-$t$ as meaningful?Show answer
It usually is not. Areas matter on $v$-$t$ and $a$-$t$ graphs, not on $x$-$t$.
What is ignoring sign of area?Show answer
Negative areas reduce net displacement. A round-trip object has zero net displacement but non-zero distance.
What is confusing straight $v$-$t$ with constant velocity?Show answer
A straight $v$-$t$ line means constant acceleration (which can be zero). Only a horizontal $v$-$t$ line means constant velocity.
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