Give examples of a one-dimensional motion where

(a) the particle moving along positive x-direction comes to rest periodically and moves forward.

(b) the particle moving along positive x-direction comes to rest periodically and moves backward.

Hint: For periodic motion, its equation must have a sine or cosine function.

Step 1: (a)The particle will be moving along positive x-direction the only if t > sint

Hence, x(t)=t-sin t

 Velocity, v(t) = dx(t)dt = 1  cost Acceleration, a(t) = dvdt = sint When t = 0; x(t) = 0 When t = π; x(t) = π>0 When t = 0; x(t) = 2π>0

Step 2: (b) Equation can be represented by

x(t) = sintv = ddtx(t) = cost

As displacement and velocity are involving sint and cost hence, these equations represent periodically.