The second hand moves 1/60th of a full rotation per second, this is equivalent to 2π/60 radians per second this is known as the objects angular velocity. the equation linking linear velocity and angular velocity is v=rω where v=linear velocity, ω=angular velocity and r=radius and so we must substitute our values in. v=(15/1000)(π/30)=0.00157 m/s which is 1.57mm/s. notice instead of just putting 15 for the radius, i did 15/1000 in order to change it from millimetres to metres, this gave me the linear velocity in m/s.
