Hi, 9 (a) Write down an equation for the displacement of a particle undergoing SHM with an amplitude equal to 8.0 cm and a frequency of 14 Hz, assuming that at t = 0 displacement is = to 8.0 cm and the particle is at rest. What I got (and this agrees with the book) was: x = 8.0 cos (28pi*t) The problem is the book then asks for the displacement, velocity and acceleration at 0.025 seconds. I simply plugged in the numbers for the displacement and got the -4.7 cm the book gets as well. My answers for the acceleration and velocity however, do not agree with the book. Can anyone help me spot my errors? a = -ω2x a = -(28pi)2x(-0.047) I get around 36 while the book gets 360. But, the difference in our velocity results is more significant: v= ±ω√(xo2-x2) v =±(28pi) √(0.082 + 0.0472) The book gets negative -5.7ms while I get positive or negative 8.16 Thanks, Peter G.