Mechanics- connected particles

[Shah 72]

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.

 

[Shah 72]

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

 

[skeeter]

a) $T - (M_L + 35)g = (M_L + 35)a$

b) $R_1 - 35g = 35a$

c) $R_2 - 15g = 15a$

d) $R_3 - 5g = 5a$

 

[Shah 72]

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

 

[Shah 72]

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

 

[skeeter]

$\dfrac{4260}{10.5} \approx 405$

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

 

[Shah 72]

$\dfrac{4260}{10.5} \approx 405$

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!