Question

Two boxes of masses of m1 = 5.4 kg and m2 = 7.8 kg respectively are on top of each other
in an elevator (on Earth), see figure 2


Figure 2. The boxes in an elevator

m1 m2

What is the resulting force on each of the boxes when the elevator moves upwards

with constant speed?

Answer 1

When elevator moves upwards with constant spedd then we have-

speed of elevator, $v=v_o$

Acceleration of elevator, $a=\dfrac{dv}{dt}=0$ (:. It's moving with constant speed)

Resulting force on the boxes 1, (equal to normal force between two boxes)

$F_1=m_1(a+g)$

but a=0,

therefore,

Resulting force on the boxes 2, (equal to normal force between box 2 and elevator)

$F_2=(m_1+m_2)(a+g)$

but a=0,

therefore, $F_2=(m_1+m_2)g=(5.4+7.8)*9.8=129.36N$

Thankyou