Note: Non-uniform plank means the CG of the plank is not at its centre a) Find the weight of the boy. b) How far is the centre of gravity of the plank from point A? Solutions: a) 300 N and b) 6.67 m Click on the video tutorial if you can’t derive the 2 equations.

Solutions: Option B As lamp X is thicker and shorter , these two factors make the resistance of X lower than Y . Recall: Length increases, R increases & cross-sectional area increases, R decreases. [R = pL/A] As both bulbs are connected to the same mains, (assume 240V), the potential difference across the bulbs are 240 V. Brightness of the bulb depends on power , P = IV or V2/R, since V is constant, I across X is higher due to lower R,hence power of X is greater than power of Y, hence X is brighter .

Solutions: Option B Whatever that goes in has to come out. With this basic concept, you will be able to solve this question easily. Ignoring the unknown branch, Total current going into O = 8A + 6A = 14A Total current going out of O = 12A + 4A = 16A Hence in order to be equal, 2A must be flowing in direction PO. Hence answer is B.

Based on individual calculations, the highest effective resistance will only be achieved if the junctions are connected at Q and S.

Density is the mass per unit volume . Common units for density are g/cm3 or kg/m3 . SI unit is kg/m3 . Density of a pure substance is fixed, regardless of it’s size! Floating and Sinking A denser (heavier) substance will sink in liquid which is less denser (lighter). A less dense (lighter) substance will float in a liquid which is denser . If substance has the same density as the liquid, it will be suspended in the liquid.

For Combined Science Physics Olevel, when constructing vector diagram, a method called  Parallelogram Method is commonly used. Parallelogram Method is used when 2 forces are known , and the resultant (net) force R , can be found. Below show 5 different variations of questions when can be solved by using Parallelogram Method: (A) Body has acceleration , forces are unbalanced , there is a resultant force R (Newton’s 2nd law) (B) Body at rest , all forces are balanced , there is no resultant force R (Newton’s 1st law) (C) Body moving at constant velocity , all forces are balanced , there is n o resultant force (Newton’s 1st law) (D) Finding unknown force (with  resultant force R  + another known force are given ) (E) Vector diagram is applicable to all vector quantities (with magnitude and direction). Not just for forces.