IB Physics SL Simple Harmonic Motion

Review IB Physics simple harmonic motion through restoring-force conditions, period and frequency, energy changes, graph interpretation and HL phase equations.

Exam points

use a=-omega^2x and restoring-force conditions to identify simple harmonic motion
calculate period, frequency, total energy or maximum speed for spring and mass systems

Covered syllabus points

C.1.1—Conditions for SHM C.1.2—SHM defining equation C.1.3—SHM quantities C.1.4—Period, frequency and angular frequency C.1.5—Energy in SHM C.1.6—SHM graphs C.1.7—SHM from circular motion

[Maximum number: 6]

This question is in two parts. Part 1 is about a thermistor circuit. Part 2 is about vibrations and waves.
Part 1 Thermistor circuit
The circuit shows a negative temperature coefficient (NTC) thermistor X and a $100 \mathrm{k} \Omega$ fixed resistor R connected across a battery.

Figure for Question C.1 Simple harmonic motion question 1 — IB Physics SL

The battery has an electromotive force (emf) of 12.0 V and negligible internal resistance.

(a)

Define simple harmonic motion (SHM).

[ 2 ]

(b)

D has mass $6.5 \times 10^{-3} \mathrm{~kg}$ and vibrates with amplitude 0.85 mm .

[ 4 ]

(i)

Calculate the maximum acceleration of D .

[ 2 ]

$\quad \omega=(2 \pi f=2 \pi \times 1250) 7854 \mathrm{rad} \mathrm{s}^{-1}$ ;

a_{0}=\left(-\omega^{2} x_{0}=-7854^{2} \times 0.85 \times 10^{-3}=\right)(-) 5.2 \times 10^{4} \mathrm{~ms}^{-2} ;

(ii)

Determine the total energy of D .

[ 2 ]

correct substitution into $E_{T}=\frac{1}{2} m \omega^{2} x_{0}{ }^{2}$ irrespective of powers of 10 ;

0.14 \text { to } 0.15 \mathrm{~J} ;

[Maximum number: 8]

(a)

State the amplitude of the oscillation.

[ 1 ]

(b)

Calculate the frequency of the oscillation.

[ 2 ]

period $=160 \mathrm{~ms}$ ;
frequency $=6.2 / 6.3 \mathrm{~Hz}$ ;

Marking guidance:

Allow ECF for incorrect period.

(c)

Determine the maximum speed of the object.

[ 2 ]

$\quad \omega=2 \pi \times 6.25$ ;
$v\left(=39.3 \times 32 \times 10^{-3}\right)=1.3\left(\mathrm{~m} \mathrm{~s}^{-1}\right) ;($ allow ECF from (a))
or
tangent drawn to graph at a point of zero displacement;
gradient calculated between 1.2 and 1.4;

(d)

The graph below shows how the displacement of the object varies with time. Sketch on the same axes a line indicating how the kinetic energy of the object varies with time. You should ignore the actual values of the kinetic energy.

Part 2 Electric and magnetic force fields

[ 3 ]

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Covered syllabus points

C.1 Simple harmonic motion question 1

Question (a)

Question (b)

Question (i)

Question (ii)

C.1 Simple harmonic motion question 2

Question (a)

Question (b)

Question (c)

Question (d)