MHB Mechanics- connected particles

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The discussion revolves around calculating various forces and reactions in a lift with three stacked boxes. The tension in the lift cable is 4260N, and the lift accelerates upward at 0.5m/s². The correct mass of the lift, including its load, is determined to be approximately 405 kg, with the lift alone weighing about 370 kg. Participants share their equations for calculating the reactions between the lift floor and the boxes, but some struggle to arrive at the textbook answers. The key takeaway emphasizes the importance of correctly interpreting the mass of the lift in relation to the total load.
Shah 72
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A box of mass 20 kg sits on the floor of a lift. A second box of mass 10kg sits on top of the first box and a third box of mass 5kg sits on top of the second box. When the tension in the lift cable is 4260N, the lift is accelerating upwards at 0.5m/s^2.
a) work out the mass of the lift.
b) work out the reaction between the floor of the lift and the first box
c) work out the reaction between the first box and the second box
d) work out the reaction between the second box and the third box.
 
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Shah 72 said:
A box of mass 20 kg sits on the floor of a lift. A second box of mass 10kg sits on top of the first box and a third box of mass 5kg sits on top of the second box. When the tension in the lift cable is 4260N, the lift is accelerating upwards at 0.5m/s^2.
a) work out the mass of the lift.
b) work out the reaction between the floor of the lift and the first box
c) work out the reaction between the first box and the second box
d) work out the reaction between the second box and the third box.
I have tried to solve this but not getting the right answers
 
a) $T - (M_L + 35)g = (M_L + 35)a$

b) $R_1 - 35g = 35a$

c) $R_2 - 15g = 15a$

d) $R_3 - 5g = 5a$
 
skeeter said:
a) $T - (M_L + 35)g = (M_L + 35)a$

b) $R_1 - 35g = 35a$

c) $R_2 - 15g = 15a$

d) $R_3 - 5g = 5a$
Thank you so so much! I will try
 
skeeter said:
a) $T - (M_L + 35)g = (M_L + 35)a$

b) $R_1 - 35g = 35a$

c) $R_2 - 15g = 15a$

d) $R_3 - 5g = 5a$
I tried the same earlier but getting the wrong. The textbook ans is 405 kg.
4260- 10m- 350= 0.5m+17.5
 
$\dfrac{4260}{10.5} \approx 405$

mass of the lift + 35kg = 405kg (actually, 406 using correct rounding)

the question should be “what is the mass of the lift plus its load”

mass of the lift alone is 370kg
 
skeeter said:
$\dfrac{4260}{10.5} \approx 405$

mass of the lift + 35kg = 405kg (actually, 406 using correct rounding)

the question should be “what is the mass of the lift plus its load”

mass of the lift alone is 370kg
Thank you very much!
 

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