An elevator car of mass starts from rest at the ground floor and moves vertically upward
PHYSICS · Multi-part · CBSE · Physics · Laws of Motion · Laws of Motion
Problem
An elevator car of mass 800kg starts from rest at the ground floor and moves vertically upward. A student of mass 60kg is standing on a bathroom-type spring balance placed on the floor of the elevator. The vertical motion of the elevator consists of three successive phases:
• Phase A: uniform acceleration of 2ms−2 for 4s,
• Phase B: motion at constant speed for 3s,
• Phase C: uniform deceleration of 1.5ms−2 until the elevator comes to rest at the next floor.
Assume g=9.8ms−2 and neglect the mass of the balance.
(i) For each phase, draw a clearly labelled free-body diagram of the student indicating all forces acting on him.
(ii) Calculate the reading shown by the spring balance during each phase.
(iii) Determine the maximum and minimum values displayed by the balance throughout the entire journey.
(iv) Compute the tension in the supporting cable of the elevator during Phases A and C.