An elevator and a man inside it have a combined mass of 1900kg what is the tension in the elevator?

Question

if it is

a)at rest

b)moving at a constant speed

c)accelerating at 1.4 m/s/s

d) if the cable can hold a max tension of 25000N is the cable in danger of breaking when going up at 1.4m/s/s

Answer 1

a) Since it is at rest only the force of weight has to be taken into consideration...

Remember the forces must balance in order for it to be stationary...

T = Tension in cable

W = Weight of elevator(with man)

T - W = 0

T = W

T = 1900(9.81) ~ 18639N

b) Again since it is moving at a constant speed... No factor is causing an increase of Force in the system...Since there is no acceleration and F = ma

This is from Newtons first law..."A particle will stay at rest or continue at a constant velocity unless acted upon by an external unbalanced force".

So again T = W

T = 1900(9.81) ~ 18639N

c) If the elevator is accelerating up...

T - W = ma

T - 1900(9.81) = 1900(1.4)

T = 21299N

If it is accelerating down...

W - T = ma

1900(9.81) - T = 1900(1.4)

T = 15979N

d) Look at the question(c) above for accelerating up ...

Since the Tension in the cable(21299N) is < 25000N

the cable will not break