Paper 2 Forces Drills

Q1 Force resolution on an incline

A box of mass $5.0\mathrm{kg}$ rests on a smooth plane inclined at $18^{\circ }$ to the horizontal.

1. Draw or describe the forces acting on the box. [2]
2. Calculate the component of the weight parallel to the plane. [2]
3. Calculate the normal contact force. [2]
4. Explain why the normal contact force is not the Newton’s third-law partner of the weight. [2]

Q2 Hooke’s law

A spring is stretched by different forces. The spring obeys Hooke’s law up to an extension of $8.0\mathrm{cm}$. A force of $3.6\mathrm{N}$ gives an extension of $6.0\mathrm{cm}$.

1. Calculate the force constant of the spring. [2]
2. Calculate the extension produced by a force of $4.8\mathrm{N}$, assuming Hooke’s law still applies. [2]
3. State what is meant by the limit of proportionality. [2]
4. Explain why the graph of force against extension may become curved beyond this limit. [2]

Q3 Moments and equilibrium

A uniform horizontal beam of length $1.20\mathrm{m}$ and weight $18.0\mathrm{N}$ is supported by a pivot at its centre. A $12.0\mathrm{N}$ load is hung $0.40\mathrm{m}$ to the left of the pivot. A second load is hung $0.30\mathrm{m}$ to the right of the pivot.

1. State the principle of moments for equilibrium. [1]
2. Calculate the second load needed for rotational equilibrium. [3]
3. Explain why the beam’s own weight does not produce a moment about the central pivot. [2]
4. State one additional condition needed for full equilibrium of the beam. [1]