Answer:
(a) 208.33 J/s
(b) 141.12 s
Explanation:
(a) Energy is the rate of doing work.
Work is the product of power and time
Work = Power × Time
Power = Work/time
where work is in joule and time is in seconds
Given that work = 6 ×
Time = 8 h = 8 × 60 × 60
= 28800 seconds
Average useful power =
= 208.33 J/s
(b) Given
mass = 2000kg , using g = 9.8 m/s2
Force = 2000 × 9.8
= 19600N
Work = Force × Distance ( considering that Work done to lift his body can be omitted because it is not considered useful output here)
Work = 19600 × 1.5
= 29,400J
Time taken = Work/Power
=
= 141.12s
≈ 2 Minutes 21 Seconds
At the rate of 208.33J/s, it will take the person 141.12 seconds to lift 2000 kg of bricks 1.50 m to a platform.