Question

In shown situation elevator is moving upward with acceleration of $5 \,m/s^2$

Column I		Column II
1	Net force acting on B	P	150 N
2	Normal reaction between A and B	Q	300 N
3	Normal reaction between B and C	R	450 N
4	Normal reaction between C and elevator	S	750 N
		T	1500 N

• A. (1)-P (2)-Q (3)-S (4)-T
• B. (1)-Q (2)-Q (3)-R (4)-T
• C. (1)-P (2)-R (3)-S (4)-S
• D. (1)-Q (2)-R (3)-R (4)-T

Answer 1

Answer: (A)

For (1) : Net force on $B = ma = (30) (5) = 150 \,N$
For (2) : FBD of $A$

$N _{ AB }-20\, g =20(5) \Rightarrow N _{ AB }=300\, N$
For (3) : FBD of $B$

$N _{ BC }- N _{ AB }-30 \,g =30(5) $
$\Rightarrow N _{ BC }=750 \,N$
For (4): For system of $A + B + C :$
$N _{ C }-100 \,g =100(5) $
$\Rightarrow N _{ C }=1500\, N$