Question

The elevator is descending with an acceleration of 2ms^-2. The mass of the block A = 0.5kg. The force exerted by the block A on block B is

(a) 2N
(b) 4N
(c) 6N
(d) 8N

Answer 1

If the elevator was stationary the force would be: mass×"g"  

Since the elevator is accelerating, the force is  

m × (g - a) = .5kg × (9.81m/s²-2m/s²) = 3.9kgm/s² = 3.9 Newtons

Answer 2

Explanation:

It is given that,

Mass of the block A, m = 0.5 kg

The elevator is descending with an acceleration of, $a=2\ m/s^2$

Value of acceleration due to gravity, $a=10\ m/s^2$

When the elevator is descending, the force acting on the object is given by :

$mg-N=ma$

N is the force exerted by the block A on block B

$N=m(g-a)$

$N=0.5\times (10-2)$

N = 4 N

So, the force exerted by the block A on block B is 4 newton. Hence, this is the required solution.