IB Physics SL A.3.7 Mechanical Energy Conservation Question Bank

Practise conserving mechanical energy to calculate speed, height and elastic or gravitational energy when losses are negligible.

Exam points

Use mechanical energy to calculate speed or height as gravitational, elastic and kinetic stores change.
Account for rotational kinetic energy or spring energy when predicting speed, height or stored energy.
Check assumptions such as negligible air resistance or rolling without slipping before conserving energy.

[Maximum number: 2]

A student strikes a tennis ball that is initially at rest so that it leaves the racquet at a speed of $64 \mathrm{~m} \mathrm{~s}^{-1}$ . The ball has a mass of 0.058 kg and the contact between the ball and the racquet lasts for 25 ms .

The student strikes the tennis ball at point P . The tennis ball is initially directed at an angle of $7.00^{\circ}$ to the horizontal.

Figure for Question A.3.7—Mechanical energy conservation question 1 — IB Physics SL

The following data are available.

Table for Question A.3.7—Mechanical energy conservation question 1 — IB Physics SL

Determine the speed of the tennis ball as it strikes the ground.

ALTERNATIVE 1

Initial KE+PE= final KE /
$\frac{1}{2} \times 0.058 \times 64^{2}+0.058 \times 9.81 \times 2.80=\frac{1}{2} \times 0.058 \times v^{2}$

ALTERNATIVE 2
$\begin{aligned} & v_{v}=<\sqrt{7.8^{2}+2 \times 9.81 \times 2.8}>=10.8<\mathrm{ms}^{-1} \gg & <v=\sqrt{63.5^{2}+10.8^{2}}> & v=64.4<\mathrm{ms}^{-1} \gg \end{aligned}$

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A.3.7—Mechanical energy conservation question 1