Chp 5: Work, energy and power

Question 1

define work done

Answer 1

product of the force and the displacement, in the direction of the force

Question 2

define principle of conservation of energy

Answer 2

The principle of conservation of energy states that the total energy of an isolated system is constant. Energy can be transformed or transferred, but the total amount of energy in any isolated system must remain constant.

Question 3

define power

Answer 3

Power is defined as the rate of work done or energy conversion with respect to time

Question 4

define joule

Answer 4

The joule is the work done by a force of 1 N on an object when it is displaced by 1 m in the direction of the force.

Question 5

Discuss the energy changes which take place when a mass suspended from a spring oscillates vertically.

Answer 5

When the mass is at the top of its oscillation, it has maximum GPE (since GPE= mgh and h is max), minimum EPE (since EPE = 1 2 𝑘𝑥 2 and x is minimum) and zero KE (since KE = 1 2 𝑚𝑣 2 and velocity v is zero) As the mass accelerates downwards towards its equilibrium position, it loses GPE, gains EPE and gains KE. Loss in GPE = gain in KE and gain in EPE. As the mass arrived at its equilibrium position, it has lost half of its total GPE (taking the lowest-position-as reference level). At the equilibrium position, the speed and hence the KE is the maximum. After the equilibrium position, the mass continues to travel down but decelerates and loses its KE and GPE while it continues to gain in EPE. At the lowest position, its GPE is zero, KE is zero and EPE is maximum due to maximum extension.