IB Physics HL A.2.19 Newton’s Second Law Applications

Practise analysing HL force and momentum systems, including drag, rockets, radiation pressure and variable acceleration.

Exam points

apply F=ma for constant-mass systems and F=Δp/Δt when momentum changes
derive resultant force from momentum change and time interval with consistent vector signs
compare Newton’s second-law forms in collisions, variable-mass or changing-force situations

[Maximum number: 2]

One end of a light spring is attached to a rigid horizontal support.

Figure for Question A.2.19—Newton’s second law forms question 1 — IB Physics HL

An object W of mass 0.15 kg is suspended from the other end of the spring. The extension x of the spring is proportional to the force F causing the extension. The force per unit extension of the spring k is $18 \mathrm{Nm}^{-1}$ .

A student pulls W down such that the extension of the spring increases by 0.040 m . The student releases W and as a result W performs simple harmonic motion (SHM).

Determine the maximum acceleration of W .

$F=(18 \times 0.04=) 0.72 \mathrm{~N}$ ;
acceleration $=\frac{0.72}{0.15}=4.8 \mathrm{~m} \mathrm{~s}^{-2}$ ;

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A.2.19—Newton’s second law forms question 1