Tips for Understanding Physics Inelastic Collision Force Mass Acceleration Energy Conservation

Physics. To some people, the subject brings chills down their spines:  long hours of brain- wracking word problems with too many given values to use and too many unknown ones to find. To other people, the subject sparks excitement, imagination, and the creativity that has brought forth the prodigious leaps in technology in the 20th and 21st centuries. So why is it that some people do not have to struggle so much in understanding physics? This could be due to an innate talent, but even talent has a method.

To start off tackling physics, read the physics problem and make a list of known and unknown values. For example, consider a problem that asks you to solve for the acceleration of an object. If the problem mentions that the object has a force of 90 N and mass of 10 kg, write down F = 90 N, m = 10 kg, and a = ?. Remember to include units!

Next, consider the chapter you are learning and write down all the equations that have been introduced up to that chapter and all the ones the professor has introduced in lecture. In the example mentioned above, F = m*a where F is force, m is mass, and a is acceleration should have been mentioned.

Then, try to rearrange the equations so that the unknown value is in terms of the given values. For the above example, we need no other equation to solve for our unknown a. Dividing F by m, we get F/m = a. Thus, plugging in our known values we get a = 90 N/ 10 kg = 9 m/s^2.  

Some aspects to note:

Know certain equations by heart. Physics is not known as a memorizing science, but there are some equations that are used in practically almost every other physical derivation. These include F = m*a where F is force, m is mass, and a is acceleration; KE = ½* m*v^2 where KE is kinetic energy, m is mass, and v is velocity; v = d/t where v is velocity, d is distance, and t is time.

Understand energy conservation. This basically means that in a closed system, the sum of the kinetic and potential energies before an event occurs should equal the sum of the kinetic and potential energies after the event occurs.  

Make sure you are using the correct form of equations. For example, for a massed object placed on a table, F = m*a where a = dv/dt. On the other, for an object that is swung around in a circle, the force would be centripetal. That is, F = m*a, but where a = v^2/ r.

Also, remember that signs, positive or negative, matter in physics. Switching the sign could make a huge difference in the final calculations. For example, consider two objects with masses m1 and m2 and velocities v1 and v2, respectively, that are undergoing inelastic collision, and we are asked to solve for the velocity after the collision. We first start with m1*v1 +m2*v2 = (m1+m2)*v , where v is the after- collision velocity. If the two objects are coming from opposite directions, the value of v1 would be positive and v2 would be negative. Making the two velocities positive or negative would yield completely different after- collision velocities.  

 Finally, ask yourself if your answer makes sense physically. For example, consider two inelastic objects with different masses coming from opposite directions and colliding with the same velocity. Does it make sense that the after- collision velocity would have the same direction as the object with the greater mass?