Paper 3 · circular motion and projectile motion
For the bob of mass 72.0 g moving at 4.5 m/s in a vertical circle of radius 50.0 cm, the centripetal force is 2.92 N. Calculate the tension in the string when the bob is at the lowest point of the circle (directly below the centre).
Model answer
3.63 N
Also accepted: 3.6 N, 3,63 N
Explanation: At the lowest point the tension supplies the centripetal force plus supports the weight: T = Mv^2/r + mg = 2.92 + (0.072 x 9.81) = 2.92 + 0.71 = 3.63 N.
Derived from ZIMSEC Physics Paper 3, June 2003, Q1