BECE Science past questions and answers

Weight always acts vertically downward, toward the centre of the Earth, no matter what surface the object rests on. In the diagram, Arrow A is the only arrow pointing straight down, so it represents the weight of the box. The other arrows represent other forces acting on the box — the normal reaction (perpendicular to the surface), friction (along the surface) and the force applied to move it — but none of these acts vertically downward, so they cannot be the weight.

In a liquid, the particles are close together but not in a fixed pattern, and they can slide past one another. This gives a liquid a definite volume but no fixed shape. Box B shows particles that are close together yet irregularly arranged, so B is the liquid. Box A shows particles in a tightly packed, regular arrangement (a solid), and box C shows particles that are far apart and random (a gas).

The wavelength is the distance between two successive identical points on a wave (for example, from one rest crossing to the next rest crossing in the same direction, or crest to crest, or trough to trough). Distance C spans one complete cycle of the wave, so it is the wavelength. The other distances are different: A is a quarter of a wavelength (crest to the next rest position), B is the amplitude (the maximum displacement from the rest position, a vertical distance), and D is half a wavelength (from a trough to the next crest).

Pressure = Force ÷ Area. Block P: Pressure = 100 N ÷ 0.5 m² = 200 Pa. Block Q: Pressure = 100 N ÷ 0.25 m² = 400 Pa. Block Q exerts more pressure (400 Pa vs 200 Pa) because the same weight is spread over a smaller area. This is why sharp objects (small area) penetrate more easily than blunt ones.

The continuous field lines that run from the left magnet straight across to the right magnet show an attraction pattern — magnetic field lines only join up like this between unlike (opposite) poles. The inner pole of the left magnet is labelled S, so the pole facing it, X, must be the opposite pole, a North pole. The other end of the right magnet, Y, is therefore a South pole. (Remember: magnetic field lines run from North to South, so here they leave X and enter the S pole of the left magnet.)

Topsoil (the A horizon) is the top layer of the soil. It contains the most humus (decomposed organic matter), the most nutrients and most of the soil organisms, which makes it the most fertile layer and the best for plant growth. The layers below it — subsoil, parent rock and bedrock — contain little or no humus.

Mechanical advantage (MA) = Load ÷ Effort = 200 N ÷ 100 N = 2. This system has one fixed pulley and one movable pulley. The movable pulley doubles the effort force, meaning you only need to apply half the load as effort. In general, the MA of a pulley system equals the number of rope sections supporting the load.

Using the principle of moments: Load × Load arm = Effort × Effort arm. So 60 N × 2 m = Effort × 3 m. Effort = 120/3 = 40 N. The lever provides a mechanical advantage because the effort arm is longer than the load arm.