Solutions: a) Refraction     b) 48.6o     c) c = 41.8o     e) 70o d) Total internal reflection has occured, as the angle of incidence is greater than critical angle and the light is traveling from a denser medium (glass) towards a less dense medium (air) Click on the video tutorial for explanation and working for part (a) and (b). Click on the video tutorial for explanation and working for part (c) to (e).

Solutions: a) 38.8o      b) 41.8o c) 51.2o . The ray does not emerge as total internal reflection has occurred. The angle of incidence is greater than critical angle and the light is traveling from a denser towards a less dense medium. Click here to view the video tutorial for working and explanation for (a) and (b). Click here to view the video tutorial for working and explanation for (c) and (d).

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.

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)

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 .