12.4

A spring scale A and a lever scale B having equal lever arms are

fastened to the roof of an elevator, and identical packages are

attached to the scales as shown. Knowing that when the elevator

moves downward with an acceleration of 1 m/s² the spring scale

indicates a load of 60 N, determine (a) the weight of the packages,

(b) the load indicated by the spring scale and the mass needed to

balance the lever scale when the elevator moves upward with an

acceleration of 1 m/s².