Question

An object is suspended by a string from the ceiling of an elevator. If the tension in the string is equal to 25 N at an instant when the elevator is accelerating downward at a rate of 2.0 , what is the mass of the suspended object

Answer 1

By Newton's second law, the net force on the object is

∑ F = T - mg = - ma

where

• T = 25 N, the tension in the string

• m is the mass of the object

• g = 9.8 m/s², the acceleration due to gravity

• a = 2.0 m/s², the acceleration of the elevator-object system

Solve for m :

25 N - m (9.8 m/s²) = - m (2.0 m/s²)

==>   m = (25 N) / (9.8 m/s² - 2.0 m/s²) ≈ 3.2 kg