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2 years ago

A lift of mass Mkg is being raised by a vertical cable attached to the top of the lift. A person of mass mkg stands on the floor inside the lift, as shown in Figure 1. The lift ascends vertically with constant acceleration 1.4 m s. The tension in the cable is 2800 N and the person experiences a constant normal reaction of magnitude 560 N from the floor of the lift. The cable is modelled as being light and inextensible, the person is modelled as a particle and air resistance is negligible.By writing an equation of motion for the person only, and an equation of motion for the lift only, find the value of M and the value of m.

Reply 2

2 years ago

Original post by GhostWalker123

A lift of mass Mkg is being raised by a vertical cable attached to the top of the lift. A person of mass mkg stands on the floor inside the lift, as shown in Figure 1. The lift ascends vertically with constant acceleration 1.4 m s. The tension in the cable is 2800 N and the person experiences a constant normal reaction of magnitude 560 N from the floor of the lift. The cable is modelled as being light and inextensible, the person is modelled as a particle and air resistance is negligible.By writing an equation of motion for the person only, and an equation of motion for the lift only, find the value of M and the value of m.

It would first be helpful to draw a diagram when attempting any mechanical problem such as this.

Motion of lift:

F=Ma

2800-Mg=M(1.4)

g=-9,8

Rearrange for M: M=250kg

Motion of person:

F=ma

560-mg=m(1.4)

g=-9,8

Rearrange for m:

Rearrange for m: m=50kg

Reply 3

1 year ago

Original post by Drogonmeister

It would first be helpful to draw a diagram when attempting any mechanical problem such as this.

Motion of lift:

F=Ma

2800-Mg=M(1.4)

g=-9,8

Rearrange for M: M=250kg

Motion of person:

F=ma

560-mg=m(1.4)

g=-9,8

Rearrange for m:

Rearrange for m: m=50kg

Motion of lift:

F=Ma

2800-Mg=M(1.4)

g=-9,8

Rearrange for M: M=250kg

Motion of person:

F=ma

560-mg=m(1.4)

g=-9,8

Rearrange for m:

Rearrange for m: m=50kg

This is wrong for the motion of the lift u have to consider newtons 3rd law and hence there should be a downwards reaction force of 560 acting on the lift from the man. Even tho we ignore the man he still exerts a force on the floor of the lift and this force will be the same as that ofbthe lift exerting 560 to the man. The reason they dont cancel is because 1 force only acts of lift and the other force only acts on man. So ur calculations shld be 2800-560-Mg=M(1.4) and so on

Original post by Drogonmeister

It would first be helpful to draw a diagram when attempting any mechanical problem such as this.

Please read forum rules - just give a hint - please edit

I've not checked whether it's correct btw

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