Paper 3 Conservation Laws in Physics Drills

Q1 System Accounting

A $2.0\mathrm{kg}$ block slides down a rough slope and loses $180\mathrm{J}$ of gravitational potential energy. Its kinetic energy increases by $120\mathrm{J}$.

1. Determine the thermal energy produced. [2]
2. Explain why mechanical energy is not conserved for the block-Earth mechanical system. [2]
3. Explain how energy conservation is restored by choosing a larger system. [2]

Q2 Inelastic Collision

A $0.50\mathrm{kg}$ trolley moving at $3.0\mathrm{m}{\mathrm{s}}^{-1}$ collides with a stationary $0.30\mathrm{kg}$ trolley. They lock together. External impulse during the collision is negligible.

1. Calculate their common velocity immediately after the collision. [3]
2. Calculate the total kinetic energy before and after the collision. [3]
3. Determine the decrease in kinetic energy. [1]
4. Explain, using a clearly defined system, why this does not violate conservation of energy. [3]
5. State one form in which the transferred kinetic energy may appear. [1]