Question

Spring balance attached to the ceiling of a
moving elevator indicates the weight of a body
which weights 980 N on ground as 1470N. The
acceleration of elevator is:
(a) 9.8 m/s2
(b) 4.9 m/s2
(c) 19.6 m/s2
(d) None​

Answer 1

Explanation:

19.6 m/s2.............

Answer 2

Case I: when the lift is at rest:

Applying Newton’s 2nd law of motion on the hanging body, we get

Spring force + gravitational force = 0

Or, -kx + mg = 0 or, kx = m*9.8 or, 49 = 9.8*m

Or, m = 49/9.8 = 5kg

(i) When the lift is moving downward:

Applying Newton’s 2nd law of motion on the hanging body, we get

mg – kx = ma or, 49 – kx = 5*5

or, kx = 49-25 = 24N

(ii) When the lift is moving downward:

Applying Newton’s 2nd law of motion on the hanging body, we get

kx-mg = ma or, kx – 49 = 5*5

or, kx = 25+49 = 74N

(iii) When lift moves with constant velocity:

Here, acceleration, a = 0

Applying Newton’s 2nd law of motion on the hanging body, we get

mg – kx = m*a or, 49 – kx= 0

or, kx = 49N