Question

A boy of mass 40 kg climbs up the stairs and reaches the roof at a height 8 metre in 5 second. Calculate:
1.force of gravity acting on the body. 2.work done bye him against the force of gravity. 3.power spent by the boy (g=10m/s^2)

Answer 1

Answer:

Force=m×a.

Given mass is equal to 40kg and as we are finding force of gravity a=g.

Hence F=40×10=400N.

Here given that displacement is 8m.

Work=F×s.

Hence W=400×8=3200Joule.

Power=Work/time

P=3200/5=640W.

Answer 2

Answer:

1. 400 N

2. 3200 J

3. 640 W

Explanation:

Given :

A body of mass 40 Kg climbs up the stairs.

Reaches the roof at a height 8 m in 5 sec.

To find :

1. Force of gravity acting on the body.

2. Work done by him against the force of gravity.

3. Power spent by the boy.

Solution :

Mass = 40 Kg

Acceleration due to gravity = 10 m/s²

Height = 8 m

Time = 5 sec

Force = Mass × Acceleration due to gravity

• 40 × 10
• 400

∴ 1. Force of gravity acting on the body is 400 N.

Work done = mgh [ Force × Displacement ]

• 400 × 8
• 3200

∴ 2. Work done is 3200 J.

Power spent = Work done ÷ Time taken

• 3200 ÷ 5
• 640

∴ 3. Power spent is 640 W.