Question about Physics Mechanies

Physics Mechanies


Mechanics



In this unit you will investigate Newton's Laws of Motion and the concepts of potential and kinetic energy. Learning about why things move will help you understand that forces are necessary to cause motion. This motion can then accomplish work. The concepts of force, friction, energy transfer, and mechanical advantage will be explored as you build simple machines and investigate there operation.


Energy
Energy is a very interesting topic to discuss because energy comes in so many different forms. In this unit we will discuss just two types of energy, potential and kinetic. First of all what is energy? Energy is that entity in our universe which allows us to do work. Work is done when a force acts through a distance. We can write this as: WORK = FORCE x DISTANCE If our force is in Newtons (about a quarter of a pound) and our distance is in meters (about three feet) then the unit of energy will be the Joule. A sixty watt light bulb uses about sixty joules of electrical energy every second. Gravitational Potential Energy is the energy that an object has due to its position in the Earth's gravitational field. If you drop a rock on your foot it hurts more the further the rock falls. This is because the higher the rock above your foot the more potential energy it has. Kinetic Energy is the energy an object has due to its mass and velocity. The faster your car is moving the more kenetic energy it has. One nice property of energy is that it can be transformed from one form to another. In experiment number two you used ravitational potential energy of the mass M1 to give the cart its kinetic energy. As you have seen the larger mass M1 was, the faster the cart moved.



Simple Machines
We have defined work to be the force used multiplied by the distance an object moves. Can we lift a ten pound object with just five pounds of force? The answer is yes if we use a simple machine to help. When we think of a machine we most often think of an electric device such as a clothes washer or a dish washer. Not all machines are electric. Experiment number three will show you how pulleys can be used to lift objects. Energy in this experiment will be conserved. The input force multiplied by the distance it moves will equal the lifted force multiplied by the distance it moves. This illustrates the property of conservation of energy. Energy can not be created nor destroyed. All we can do is change it from one form to another.





(1)x(root(1.2x10^-12)) = (1)x-(root(1.2x10^-12)) + 12V(c)
V(c) = (root(1.2x10^-12))/6
neutron KE loss = carbon neuclei KE gain (Elastic collision)
neutron KE loss in 1 collision = 0.5(12)((root(1.2x10^-12))/6)^2
= 2x10^-13 J

b) Total KE loss of the neutron = 6x10^-13 - 6x10^-21 = 6x10^-13J
KE loss of the neutron in 1 collision = 2x10^-13J
Number of collisions = 6x10^-13 / 2x10^-13

(i) Elastic collision is the collision process that, apart from momentum, kinetic energies of the collising objects are conserved. That is, there is no loss of kinetic energy in the process.
(ii) Inelastic collision is the collision process in which only momentum is conserved, but NOT kinetic energies of the colliding objects.
If the collision is perfectly (or completely) inelastic, the two colliding objects will adhere to each other after collision.
Examples:
(i) the collision between two table-tennis balls (ping pong balls) is close to an elastic collision;
(ii) the collision between two motor vehicles is generally an elastic collision, as there is energy lost in the form of heat and sound.