Work done W = F x d Only when there is distance moved in the direction of the force , there is work done. (i.e. look for the distance parallel to the force)

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.

Double-insulated appliances are common around us. The air purifiers in our classroom are one good example. In these appliances, only two wires are needed, namely Live and Neutral wires . Earth wire is not required as the casing is made of insulator like plastic for this case. The classic air purifier in our classroom The “double squares” symbol means that this appliance is double-insulated. As you see, the earth wire is not required.

The concepts needed to solve such questions Length increases, resistance increases and vice versa. Finding resistors in parallel and in series.

Solutions: Option B Without the current in the river, the time taken for the swimmer to reach Q is 50s. This is based on the vertical constant speed of 1.2 m/s and veritcal (width of river) distance. With the current, which is constant 1.0 m/s, the swimmer will be drifted downstream. But the time taken to reach R from P is still 50s. So with the same 50s, you can calculate the horizontal distance based on the horizontal current speed of 1.0 m/s.

Solutions: Option B Key concepts: Both balls are free-falling, hence both will experience the same acceleration due to gravity 10 m/s2.

Solutions: Option B