cos(2 but) + 4.5 where d is the distance from a wall in metres, and t is the time in seconds. a) State the initial amplitude and the period of the pendulum. b) After how long will the amplitude be reduced to 50% of its initial value? c) Determine a function that gives the speed of the pendulum bob as a function of time. d) At what time is the speed 0? 4. The displacement of the bob of a pendulum is given by d(t) = 1.3e cos(2/1.5mt) + 4.5 where d is the distance from a wall in metres, and t is the time in seconds. a) State the initial amplitude and the period of the pendulum. b) After how long will the amplitude be reduced to 50% of its initial value? c) Determine a function that gives the speed of the pendulum bob as a function of time. d) At what time is the speed 0?