Magnitude of the centripetal force exerted by the string on the
ball to produce this acceleration which is given as :
centripetal force given by, Fc = m v2 /
r                                                    Â
{ eq.1 }
centripetal force given by, ac = v2 /
r                                                             Â
{ eq.2 }
equating above two eq. we get
Fc = m
ac                                                                     Â
{ eq.3 }
where, m = mass of the ball = 0.25 kg
ac = centripetal acceleration = 4 m/s2
inserting the values in eq.3,
Fc = (0.25 kg) (4 m/s2)
Fc = 1 N
