IB Physics SL A.1.5 Instantaneous and Average Values

Practise distinguishing instantaneous from average speed, velocity and acceleration by using tangents, total path length, net displacement and the relevant time interval.

Exam points

calculate average speed from total distance over total time and average velocity from displacement over time
estimate an instantaneous velocity by drawing a tangent and calculating its gradient at the stated time
compare an instantaneous graph value with an interval average without substituting one for the other

[Maximum number: 3]

This question is in two parts. Part 1 is about kinematics and gravitation. Part 2 is about radioactivity.
Part 1 Kinematics and gravitation
A ball is released near the surface of the Moon at time t=0. The point of release is on a straight line between the centre of Earth and the centre of the Moon. The graph below shows the variation with time t of the displacement s of the ball from the point of release.

Figure for Question A.1.5—Instantaneous and average values question 1 — IB Physics SL

Use the graph to

estimate the velocity of the ball at $t=0.80 \mathrm{~s}$ .

tangent drawn to curve at 0.80 s ;
correct calculation of gradient of tangent drawn;
$-1.3 \pm 0.1 \mathrm{~m} \mathrm{~s}^{-1}$ or $1.3 \pm 0.1 \mathrm{~m} \mathrm{~s}^{-1}$ downwards;
or
correct coordinates used from the graph;
substitution into a correct equation;
$-1.3 \pm 0.1 \mathrm{~m} \mathrm{~s}^{-1}$ or $1.3 \pm 0.1 \mathrm{~m} \mathrm{~s}^{-1}$ downwards;

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A.1.5—Instantaneous and average values question 1