Question

A 50 kg boy stands on platform spring scale in a lift that is going down with constant speed 3 metre per second if the lift is brought to rest by constant acceleration in distance of 9 m what does the scale read during this period

Answer 1

initial speed , u = 3m/s
distance covered , s = 9m
now, v² = u² + 2as
the lift brought to rest by constant acceleration in distance of 9m.
hence, final speed , v = 0
so, 0 = 3² + 2a × 9
a = -0.5 m/s²
negative sign shows that acceleration is downward.

now, net acceleration, A = -(a + g)
= -(0.5 + 9.8) = -10.3 m/s²

hence, reading = mA
= 50 × 10.3
= 515N

Answer 2

Answer:515N

Explanation:Initial speed , u = 3m/s

distance covered , s = 9m

now, v² = u² + 2as

the lift brought to rest by constant acceleration in distance of 9m.

hence, final speed , v = 0

so, 0 = 3² + 2a × 9

a = -0.5 m/s²

negative sign shows that acceleration is downward.

now, net acceleration, A = -(a + g)

= -(0.5 + 9.8) = -10.3 m/s²

hence, reading = mA

= 50 × 10.3

= 515N