IB Physics SL A.3.9 Kinetic energy

Practise calculating kinetic energy and relating it to mass, speed, momentum and graph-based work in particle and object motion.

Exam points

calculate speed from KE after finding work done, for example using the area under a force–distance graph
link KE and momentum algebraically to compare moving objects when masses or energy ratios are given
convert particle energy gained in eV or J into speed using 1/2 mv^2, with careful unit substitution

[Maximum number: 2]

A toy rocket is made from a plastic bottle that contains some water.

Air is pumped into the vertical bottle until the pressure inside forces water and air out of the bottle. The bottle then travels vertically upwards.

Figure for Question A.3.9—Kinetic energy question 1 — IB Physics SL

The air-water mixture is called the propellant.
The variation with time of the vertical velocity of the bottle is shown.

The bottle reaches its highest point at time $T_{1}$ on the graph and returns to the ground at time $T_{2}$ . The bottle then bounces. The motion of the bottle after the bounce is shown as a dashed line.

The bottle bounces when it returns to the ground.

Calculate the fraction of the kinetic energy of the bottle that remains after the bounce.

Attempt to evaluate KE ratio as $\left(\frac{v_{\text {final }}}{v_{\text {initial }}}\right)^{2}$

« $\left(\frac{4.5}{10}\right)^{2}=$ 》 0.20 OR 20 % OR $\frac{1}{5}$

Marking guidance:

Accept ± 0.5 velocity values from graph

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A.3.9—Kinetic energy question 1