A spring balance fastened to the roof of a lift accelerating upwards indicates `120 N` as the weight of a `80 N` body. The acceleration of the lift is `(g = 10 m//s^(2))`.

Options

A. `5 m//s^(2)` upwards
B. `(20)/(3) m//s^(2)` upwards
C. `(10)/(3) m//s^(2)` upwards
D. `5 m//s^(2)` downwards

Answer

A

Explanation

`m (g + a) = 120 " " mg = 80`
`mg + ma = 120 " " m = 8`
`80 + ma = 120`
`ma = 40`
`a = (40)/(8) = 5 m//s^(2)`