作业帮 > 英语 > 作业

this is an AS physics question about acceleration and veloci

来源:学生作业帮 编辑:作业帮 分类:英语作业 时间:2024/11/09 01:45:31
this is an AS physics question about acceleration and velocity.
a ball is kicked towards goal posts from a position 20m from and directly in front of the posts.the ball takeds 0.60s from the time it is kicked to pass over the cross-bar,2.5m above the ground .the ball is at its maximum height as it passes over the cross-bar.you may ignore air resistance.
a)calculate the ball's horizontal component of velocity.
b)calculate the vertical component of the velocity of the ball immediately after it is kicked.
c)determine the magnitude of the initial velocity of the ball immediately after it is kicked.
d)determine the angle above the horizontal at which the ball is kicked.
Hi there.I just got an A* in the entire A level Physics course,so my answer should be trustworthy.:) The reason why I wrote my answer in English was to make it consistent with your question.:P
First of all,the only force exerted on the ball after the kick is the gravitational attraction force.In other words,it experiences free fall.So:
a) Firstly look in the horizontal direction.Assuming that the air resistance is negligible,then there is no horizontal force acting on the ball.Thus the horizontal acceleration is zero (according to Newton's II law).Using v=s/t in the horizontal direction,vh=20/0.6 = 33.3 m/s (vh stands for hotizontal velocity)
b) Now let's look in the vertical direction upwards,the acceleration a of the ball is -9.81m/s^2.(Notice the negative sign,it is there because gravity directs downwards but we are now looking at the upward direction.) Using one of the SUVAT equations s=ut+1/2 at^2 (s=2.5m,t=0.6s,a=-9.81 m/s^2),then we can find out the value for u,which is the initial vertical component of the ball's velocity.
c) Resolving backwards the horizontal and vertical components of the velocity using Pythagora's thereom:V^2= vh^2+u^2.Substitute the values of vh and u which have been worked out previously,you can get the value of V (the magnitude of the initial velocity).
d) Draw a vector triangle for this question would help you a lot.Vertically up is the value of u,in the horizontal direction it is the vector of vh.Complete this triangle.Then you get tan α (the angle above the horizontal) = u / vh.