Reflection Feng

This is my reflection on what I've learned in the Vector Kinematics unit, the difficulties that I've encountered, and my strengths and weaknesses in problem-solving skills.


What I Learned About....

I learned about how natural forces like winds and currents can affect the intended direction of a plane or a boat in operation. I've also understood the concept of relative motion, that is, when two velocities are heading in different directions, one has a relative velocity to the other. One example would be the velocity of a person on a train relative to the ground; the equation would be Vpg=Vpt+Vtg. There was also 2-D relative motion for only two objects that I came across with, and its equation was Vab=-Vba. To "a", the velocity of "b" is the same as "b" views "a", but direction is the opposite. For projectile motion, I learned about horizontally launched projectiles where the y components of the initial velocity is 0. The other projectile type was a complete parabola where the initial vertical velocity equals a negative final vertical velocity (Vyf=-Vyi).


Obstacles I Encountered....

When drawing a labelled diagram for a relative motion question, I found some difficulties in identifying the resultant velocity and so drawing the correct triangle for solving the problem. I thought the resultant velocity was always the hypotenuse of the right triangle, but I realized that wasn't always the case when I came across with this one question. It says "the captain of an airliner wishes to proceed due west, and the cuising speed of the plaine is 245m/s relative to the air in the southwest direction." The resultant was the Vairliner relative to the ground but I thought it was the other vector, hence drew the wrong the diagram and set up the wrong equation. It was this problem which I struggled with for a while.


My Problem-Solving Skills....

My strengths in solving kinematics problems were being able to identify all the vector components in a question (eg. Vpg, Vpt, Vtg in a question asking the velocity of a person on a train relative to the ground), including their directions, so that a diagram could be drawn to help me visualize the motion happening. I was also rather good at using trigonometry, sine law and cosine law to calculate the velocity and direction wanted. For instance, I would use "tan" to get the hypotenuse (representing the resultant velocity) given the velocity of the adjacent side.

On the other hand, my weaknesses lied in solving projectile motion launched at an angle at a height. Especially for finding the total time of motion, at first I tried to split the trajectory into two parts (one being a complete parabola and the other being the last part of the projectile going down) and calculate the time for each part and add them together. A sample question would be: a projectile is thrown from a 60.0 m cliff with 50.0 m/s at an angle of 30.0 degree, what's the time of flight? Despite getting the same answer as simply using a kinematics formula, I went the longer way. In summary, I needed to be more familiar with projectile launched at an angle and a height.