WAEC Physics 2013 Theory — Question 11

Model answer

(a) The triangle law of vector addition states that if three forces are in equilibrium, they can be represented in magnitude and direction by the three sides of a triangle taken in order (i.e. if two vectors AB and BC represent two sides of a triangle in that order, then the third side AC represents the resultant of vectors AB and BC — the resultant vector is the line joining the tail of the first vector to the head of the second vector). (b) Physical quantities associated with equations of motion include: (i) distance or displacement, (ii) speed or velocity, (iii) acceleration, (iv) time. (c) On the same axes, potential energy and kinetic energy in SHM both oscillate periodically (with the same period as the motion but twice the frequency), always summing to a constant total energy: kinetic energy is maximum (and PE is zero) at the equilibrium position, while PE is maximum (and KE is zero) at maximum displacement (amplitude); the two curves are therefore mirror images of each other over time, both varying between zero and the maximum energy value.