Paper 2 Dynamics Drills

Q1 Connected bodies

Two blocks of masses $2.0\mathrm{kg}$ and $3.0\mathrm{kg}$ are connected by a light string on a smooth horizontal surface. A horizontal force of $15.0\mathrm{N}$ pulls the $3.0\mathrm{kg}$ block.

1. Calculate the acceleration of the two-block system. [2]
2. Calculate the tension in the string. [3]
3. Explain why the tension is not included when the two blocks are treated as one combined system. [2]

Q2 Lift motion

A student of mass $58.0\mathrm{kg}$ stands on a scale in a lift.

1. Calculate the scale reading when the lift is stationary. [1]
2. Calculate the scale reading when the lift accelerates upward at $1.20\mathrm{m}{\mathrm{s}}^{-2}$. [3]
3. Calculate the scale reading when the lift accelerates downward at $1.20\mathrm{m}{\mathrm{s}}^{-2}$. [3]
4. Explain what the scale reads during ideal free fall. [2]

Q3 Impulse

A $0.060\mathrm{kg}$ tennis ball travelling horizontally at $24\mathrm{m}{\mathrm{s}}^{-1}$ strikes a racket and rebounds horizontally at $18\mathrm{m}{\mathrm{s}}^{-1}$ in the opposite direction. The contact time is $4.0\mathrm{ms}$.

1. Taking the initial direction as positive, calculate the change in momentum of the ball. [3]
2. Calculate the average force exerted on the ball. [2]
3. State the direction of this average force. [1]
4. Explain why the force exerted by the ball on the racket has the same magnitude as the force exerted by the racket on the ball. [2]