You are Here: Home >< Physics

Mechanics question watch

1. 2 boxes A ( 110kg) and B (190kg) sit on the floor of a lift ( 1700kg). Box A sits on Box B. The lift is supported by a light inextensible cable and is descending at a constant acceleration 1.8m/s^2
The tension at the cable ?
Force exerted by box B on box A ?
I got the tension = to 1600N but the MS of the textbook says 3600 ! And i think im lost for the second question. Can someone help?
2. (Original post by Physics Enemy)
m = 2000 kg, accelerating downward reduces tension by 1.8m. So T = mg - 1.8m = 8m = 16,000 N

For the last bit, force by B on A equals force by A on B i.e) A's effective weight, so 110 x 8 = 880 N
U mean 110x 1.8? *
3. (Original post by Tirawi19)
...
(Original post by Physics Enemy)
m = 2000 kg, accelerating downward reduces tension by 1.8m. So T = mg - 1.8m = 8m = 16,000 N

For the last bit, force by B on A equals force by A on B i.e) A's effective weight, so 110 x 8 = 880 N
I re-did the Q by drawing a diagram and doing it properly, to see if I made a mistake earlier.

Forces on the lift: W - T = ma
=> 2000g - T = 2000 x 1.8
=> T = 2000 x 8
=> T = 16,000 N

Forces on box a: W_a - R_a = m_a x 1.8
=> 110g - 110 x 1.8 = R_a
=> R_a = 110 x 8
=> R_a = 880 N

So I stand by my answers from before

Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: August 12, 2017
Today on TSR

Exam Jam 2018

Join thousands of students this half term

Solo - A Star Wars Story

Poll

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE