A boy stands on a weighing machine inside a lift. When the lift is going down with acceleration g/4, the machine shows a reading 30 kgf. When the lift goes upwards with acceleration g/4, the reading would be

Question

A boy stands on a weighing machine inside a lift. When the lift is going down with acceleration g/4, the machine shows a reading 30 kgf. When the lift goes upwards with acceleration g/4, the reading would be (A) 18 kgf (B) 37.5 kgf (C) 50 kgf (D) 67.5 kgf

Tardigrade Admin · Accepted Answer

While going down, machine reading is 30 kgf. ⇒ mg-N=m((g/4)); mg-30g=(mg/4) ;3 (mg/4)=30g m=(30×4/3)=40 kg While going up, the reaction would be N'-mg=m (g/4) N'=5 (mg/4)=(5/4) (40 kg)g ⇒ N'=50 kgf.

Q. A boy stands on a weighing machine inside a lift. When the lift is going down with acceleration g/4, the machine shows a reading 30kgf. When the lift goes upwards with acceleration g/4, the reading would be

18 kgf

37.5 kgf

50 kgf

67.5 kgf

While going down, machine reading is 30 kgf. ⇒mg−N=m(4g​); mg−30g=4mg​;34mg​=30g m=330×4​=40kg While going up, the reaction would be N′−mg=m4g​ N′=54mg​=45​(40kg)g ⇒N′=50kgf.

Q. A boy stands on a weighing machine inside a lift. When the lift is going down with acceleration $g /4$ , the machine shows a reading $30 k g f$ . When the lift goes upwards with acceleration $g /4$ , the reading would be