Question

A platform of mass 2kg is supported by a spring of negligible mass as shown. The platform oscillates with a period of 3 s when the platform is pushed down and released. What must be the mass of a block that when placed on the platform doubles the period of oscillation to 6 s? 

(A) 1kg 

(B) 2kg 

(C) 4kg 

(D) 6kg 

(E) 8kg

Answer 1

Correct option (D) 6kg

Based on T = 2π√(m/k), in order to double the period, the mass would have to be increased by 4x the original amount. Here is the tricky part …. you are to increase the mass to 4 x its original value by adding mass the to 2kg tray. So to make the total mass have a value of 8 kg, only 6 kg of extra mass would need to be added to the tray.