In Fig. (i), the man walks 2 m carrying a mass of 15 kg on his hand. I

1.	In Fig. (i), the man walks 2 m carrying a mass of 15 kg on his hand. In Fig. (ii), he walks the same distancepulling the rope behind him. The rope goes over a pulley, and a mass of 15 kg hangs at its other endin which case is the work done by gravity is greater ?15 kgf15 kg
Answer» CASE (i) : force applied on 15 kg mass , F = mg = 15kg × 9.8 m/s² = 147 N [ vertically downward ] DISPLACEMENT of mass , s = 2m [ horizontally west direction ] so, angle between force and displacement vector, Φ = 90° we know, work DONE = F.scosΦ = 147 × 2 × cos90° = 0 case (ii) : force applied on mass, F = TENSION in rope = WEIGHT of body = mg = 147 N [ horizontally west direction ] displacement , s = 2m [ horizontally west direction ] so, angle between F and s , Φ = 0° so, work done = F.scosΦ = 147 × 2 × 1 = 294 J hence, in case (ii), more work is done.

In Fig. (i), the man walks 2 m carrying a mass of 15 kg on his hand. In Fig. (ii), he walks the same distancepulling the rope behind him. The rope goes over a pulley, and a mass of 15 kg hangs at its other endin which case is the work done by gravity is greater ?15 kgf15 kg

Answer»

CASE (i) : force applied on 15 kg mass , F = mg = 15kg × 9.8 m/s² = 147 N [ vertically downward ]

DISPLACEMENT of mass , s = 2m [ horizontally west direction ]

so, angle between force and displacement vector, Φ = 90°

we know,

work DONE = F.scosΦ

= 147 × 2 × cos90° = 0

case (ii) : force applied on mass, F = TENSION in rope = WEIGHT of body = mg

= 147 N [ horizontally west direction ]

displacement , s = 2m [ horizontally west direction ]

so, angle between F and s , Φ = 0°

so, work done = F.scosΦ

= 147 × 2 × 1 = 294 J

hence, in case (ii), more work is done.

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