Question

A pendulum bob of 2kg mass, displaced through an angle of 60°, Oscillates continuously about its rest position. If the length of the pendulum is 80cm, What is the maximum kinetic energy attained by the bob?

Answer 1

here as we know that there is no frictional loss

so here we will have sum of gravitational potential energy and kinetic energy will remain constant

so we can say that

$U_i = K_f$

at initial point gravitational potential energy must be equal to maximum kinetic energy at its mean position

so now we will have

$KE_{max} = mgL(1-cos\theta)$

here we know that

m = 2kg

L = 80 cm

$\theta = 60 degree$

now from above equation

$KE_{max} = 2(9.8)(0.80)(1 - cos60)$

$KE_{max} = 7.84 J$