Work, energy and the conservation law
Answers are for parents and teachers.
1
A force F = 30 N moves a body 6 m at an angle of 60° to the displacement (cos60° = 0.5). What is the work (J)?
90
2
A 4 kg body falls from rest from 10 m (g = 10 m/s²). What is its speed on hitting the ground (m/s)? (υ = √(2gh); to 0.1)
14.1
3
Useful work is 450 J and efficiency is 75%. What is the total work (J)?
600
4
A 20 kg load is raised 2 m (g = 10 m/s²). What is the useful work (J)?
400
5
Why does the work of gravity have opposite signs for a body going up and a body coming down?
Going up the force is opposite to the displacement (cos180° = –1), coming down it is in the same direction (cos0° = 1).