Question

Will it be possible to find the initial velocity using Newton

Answer 1

1

The laws of conservation of energy and momentum are among the most fundamental and useful laws of physics. They aid in the solution of many mechanics problems and come up frequently in many fields of science. What these laws say is that if there are no net forces on a system, then that system will have the same momentum, p = mv, at all times. In addition, if there are no external or internal forces acting in or on a system, then the energy of that system will remain constant. Newton's First Law is hidden in these conservation laws. Newton's First Law states that bodies at rest will remain at rest as long as no forces act upon them, and bodies in motion will remain in motion as long as no forces act upon them. As one can see, Newton's First Law is a statement about conservation of momentum and energy. Things stay the same, as long as they are left alone.

Despite their fundamental nature, the conservation laws are often difficult to observe in ordinary experiences, primarily because of the presence of friction. Friction between moving bodies and their surroundings means there are external forces acting on the system, therefore, the conservation laws do not apply. So, to observe the conservation laws, friction must be eliminated as much as possible.

This lab will deal primarily with the conservation laws as they apply to collisions between material objects. These collisions can be divided into two different classes; elastic collisions and inelastic collisions. If the kinetic energy of a particle is the same before and after the collision, then the collision is said to be elastic. Notice the reference to particles. Solid bodies are not particles, but have structure. If the collision, however, leaves there structure unchanged, they can be treated as particles. For the other type of collision, energy will flow between the two objects, and the kinetic energy will not be conserved. In this case, the collision is said to be inelastic. Note that in the absence of friction, the momentum will be conserved in both types of collisions.

In one dimension, the conditions before and after an elastic collision between two bodies of masses m₁ and m₂, initial velocities v_1iand v_2i,and final velocities v_1f and v_2f, are given by

(Kinetic Energy)

(Momentum)

For an inelastic collision only the momentum equation is valid.

2

Using conservation of energy it is possible to find the initial velocity of the ball. In this

ball-pendulum system we cannot use the conservation of mechanical energy to relate the

quantities because energy is transferred from mechanical to nonconservative forces.