Question

a A girl weighing 30 kgf climbs up 30 steps, each 20 cm high in
minutes. Calculate the work done by her against gravity.​

Answer 1

Given info : A girl weighing 30 kgf climbs up 30 steps, each 20 cm high in 3 minutes

To find : The work done by her against gravity is...

solution : weight of girl, W = 30 kgf = 30 kg × 10 m/s² = 300 N [ acceleration due to gravity g = 10 m/s²]

total distance covered, S = 30 steps = 30 × 20cm = 600 cm = 6 m

work done against gravity= weight of girl × total distance covered × cosθ

where θ is angle between force and displacement.

here you see, girl climbs up so displacement directs upwards while her weight acts downwards.

so, angle between them, θ = 180°

now work done against gravity = 300 N × 6m × cos180° = -1800 J

Therefore magnitude of work done against gravity is 1800 J.