A 50 kg boy stands on a platform spring scale in a lift that is going down with a constant speed ` 3 ms^(-1)`. If the lift is brought to rest by a constant deceleration in a distance of 9 m, what does the scale read during this period ? ( Take , `g=9.8 ms^(-2)`)

Options

A. 500 N
B. 465 N
C. 515 N
D. zero

Answer

C

Explanation

(c ) Given, `v=0,u=3 ms^(-2)`
so using, `v^(2)=u^(2)-2as`
`0=(3)^(2)=2a(9)`
`therefore a(1)/(2)=0.5 ms^(-2)` (upwards)
` N=m(g+a)=50(9.8+0.5)=515N`