Weight is the gravitational force acting on a mass, found by multiplying the mass by the acceleration due to gravity. The symbol g represents how quickly gravity accelerates a mass near Earth’s surface, not how fast the object is moving (that’s velocity), nor a distance, nor the mass itself. The value of g is about 9.8 m/s^2, so heavier objects have greater weight because the same acceleration acts on more mass.

Key idea: efficiency is the fraction of input energy that becomes light. If 20% of the electrical energy is converted to light, you multiply the input energy by 0.20. So with 5 joules of electrical energy, light energy produced = 5 × 0.20 = 1 joule. The remaining energy isn’t light (it's wasted as heat or other losses). The other numbers would come from using different fractions (for example, 0.10 would give 0.5 J, 0.80 would give 4 J, and 0.40 would give 2 J).

A generator converts mechanical energy into electrical energy through electromagnetic induction. When the magnet and coil move relative to each other, the magnetic flux through the coil changes. This changing flux induces an electromotive force in the coil, causing current to flow in a closed circuit. The energy that drives this induction comes from the mechanical energy you supply to keep the rotation going, so kinetic/mechanical energy is transformed into electrical energy. Some energy may be lost as heat due to resistance, but the primary transformation is mechanical energy to electrical energy. This differs from conversions like chemical energy to electrical, thermal energy to electrical, or nuclear energy to kinetic energy, which require different devices or setups.

When something falls, gravity transfers its stored potential energy into kinetic energy (assuming no air resistance). Because energy is conserved, the kinetic energy just before impact equals the initial gravitational potential energy: KE = m g h. Here, m = 1.0 kg, g ≈ 9.8 m/s^2, and h = 2.0 m, so KE = 1 × 9.8 × 2 = 19.6 J. The other numbers would come from different fall heights: 9.8 J if it fell 1 m, 39.2 J if it fell 4 m, and 0 J only if there was no fall. If you want the speed just before impact, v = sqrt(2 g h) ≈ sqrt(39.2) ≈ 6.3 m/s.