Reflection by Stanley
In the chapter of projectile motion, I learnt how to calculate the velocity of throwing things in the influence of gravity. Because of the gravity and other vectors work on the object, its speed and direction always being different and it is the difficulty to solve these questions. In the quiz, I lost the most marks in final question, because I choose the wrong formula, carelessness always makes me losing marks on details. Otherwise, I can solve questions in a short time correctly.(Stanley Wang)
Comment by Hanwen Xing: Try to be a calm guy....just like me.....^ ^
Comment by Edmund Zhai: You will get a very high mark.
Comment by Hanwen Xing: Try to be a calm guy....just like me.....^ ^
Comment by Edmund Zhai: You will get a very high mark.
REFLECTION by Hanwen
I have learnt projectile motion for the past several weeks, i found that this part is difficult to understand and master. and i believe the only solution is to think deeper and find the essences of those concepts. My problem solving skills are satisfying. Even though i could figure the problems out fast and properly, i still make mistakes because of my carelessness. For example, I can solve the problems generally correctly, but the unexpected flaws in my writing process always keep me away from a perfect mark. (Hanwen)
Comment by Edmund Zhai: Can you share your problem-solving skills. You got over-perfect
Comment by Stanley Wang: Yeah you got 101 percents...and you calculate so fast.
Reflection by Edmund Zhai
For this chapter, I learned about the fundamental concepts of vector. With the knowledge of vectors, I explored the relative velocity, the two dimensional kinematics and eventually the projectile motion in different situations. I had difficulties with the relative velocity because I sometimes have trouble determining the angle and the resultant velocity. For solving skills, when I do projectile motion, I always set two columns: the horizontal part and the vertical part and solve with the data given and calculated. My strength is the projectile motion: I got full mark in the two written projectile motion. My weakness is the relative velocity: for the 5 multiple choices I got wrong, 3 of them are questions on relative velocity. (Edmund Zhai)
Comment by Hanwen Xing: Maybe....the best way to improve is to think everything one step deeper....Trust me that works :)
Comment by Stanley Wang: Maybe one more check?
Comment by Hanwen Xing: Maybe....the best way to improve is to think everything one step deeper....Trust me that works :)
Comment by Stanley Wang: Maybe one more check?
B: Project: The projectile motion of shot put
The two-dimensional projectile motion is present in the sports of shot put (the path of the ball from leaving the athlete's hand to landing on the floor) The trace of the ball could be simplified by a parabola. And we will explain the projectile motion and its underlying connection with shot put.
Definition of projectile motion
Projectile motion is a form of motion where a particle (called a projectile) is thrown obliquely near the earth's surface, it moves along a curved path under the action of gravity. The path followed by a projectile is called its trajectory. (from Wikipedia)
This following image illustrates three important factors of projectile motion---the angle, the initial velocity and the range.
This following image illustrates three important factors of projectile motion---the angle, the initial velocity and the range.
Movement of Shot put
As illustrated in the graph, the path is a parabola shape projectile motion. The ball starting from a specific height rises to its highest point and drops back to the ground. The change in its horizontal position is the range, which is the distance that referees measure. After the ball is thrown, the horizontal velocity remains constant. The vertical velocity, however, experience a downward acceleration of -9.8m/s^2 due to gravity. This downward force begins to affect the ball as soon as the ball is released. The vertical velocity slows gradually and becomes zero at the maximum height. After reaching the top, the ball falls down to the ground, also experiencing an acceleration of -9.8m/s^2. At the same time interval, the horizontal velocity will bring the ball over a range depending on the initial velocity and angle.
How are the physics concepts apply in the shot put?
The world record of shot put was made by Randy Barnes,which is 23.12 m, one day I push the shot with an initial angle of 34 degree. So what is the minimum velocity required if i want to break the record?
Since the motion of the shot can be considered as a projectile motion, so we can solve the question by using projectile formulas.
cos34V=gt
(t is the half of the time,since Vy=0 at the highest point, so we can get cos34V=gt)
sin34V(2t)=R
(the horizontal velocity is constant, so the range can be expressed as sin34V(2t) )
t=cos34V/g
(now express t by V and g)
R=2cos34sin34V^2/g
(and plug t into this equation)
23.12=2sin34cos34V^2/9.8
(CALCULATION)
V=15.6m/s
Since the motion of the shot can be considered as a projectile motion, so we can solve the question by using projectile formulas.
cos34V=gt
(t is the half of the time,since Vy=0 at the highest point, so we can get cos34V=gt)
sin34V(2t)=R
(the horizontal velocity is constant, so the range can be expressed as sin34V(2t) )
t=cos34V/g
(now express t by V and g)
R=2cos34sin34V^2/g
(and plug t into this equation)
23.12=2sin34cos34V^2/9.8
(CALCULATION)
V=15.6m/s
In the previous example, a shot put problem in real life can be solved by applying the knowledge of Projectile motion