Physics problem: would you mind to teach me how to do this question, thanks.?

A) since no distance is done in line with force, no work is done.
B)  F = m v² / r = m * ω² / r
ω = √Fr/m = √(5*0.40m/0.20kg)  ((in KMS system))
Round answer to 1 sigfig since 5 N only had 1 sigfig!!

(a)  No work is done by the tension in the string, as the motion is perpendicular to that force.

(b)  The centrifugal force is mv^2/r, or mr(omega)^2, where omega is the angular speed.  So if we set
(5 N) = (0.200 kg)(0.40 m) * (omega)^2, we get
omega^2 = 62.5 s^(-2) =>
omega = around 8 rad/s but use a calculator.