Mechanical Engineering - Engineering Mechanics - Discussion

Energy conservation should not be confused with linear momentum. Whilst one concerns itself with the fact that energy cannot be created or lost, the other is focused on changes that can happen within a system of masses moving in a particular direction when external forces are applied. Is there a change in system energy when momentum changes? Possibly.

Kinetic energy of a moving system of masses is 0.5 x (m1 x v1^2 + m2 x v2^2 x ......mn x vn^2). The mass of objects will not change unless some molecular distortion occurs which is not treated herein. However, the velocity can reduce or increase.

Hence, the system energy can go up or go down. However, if this is happening in a closed system, the kinetic energy lost becomes gained as heat energy. Hence, total energy remains unchanged. But if this is not a closed system, then energy is exchanged across our artificial boundary which contains the system of masses, and therefore system energy changes.

So, the key word here for the statement to be true is whether the system is CLOSED or OPEN. And, since we were not informed on this, the assumption is that it is an OPEN system in which case the correct answer is FALSE because the energy conservation principle will NOT hold in an OPEN system.

According to conservation of energy principle. Energy can neither be created nor be destroyed. It can only be transferred from one form to another.

False.

According to the law of conservation of momentum, the total momentum of a system remains constant in a given direction if no external force acts on the system in that direction.

I am not getting this, please explain me.

The law of conservation of energy, first formulated in the nineteenth century, is a law of physics. It states that the total amount of energy in an isolated system remains constant over time. The total energy is said to be conserved over time. For an isolated system, this law means that energy can change its location within the system, and that it can change form within the system, for instance chemical energy can become kinetic energy, but that energy can be neither created nor destroyed.

From: http://en.wikipedia.org/wiki/Conservation_of_energy

True, when no change in momentum takes place either we say statically condition.

The principle of law of conservation says that energy neither created nor destroyed.

Energy neither created nor to be destroyed but it is a form of energy according to principle of the law of conservation of energy.

According to the conservation of energy, the energy neither be created and nor be destroyed it can transform one state to another state only.

Principle of conservation of energy states that energy can neither be created nor be destroyed.