HibaSyed Posted February 1, 2013 Share Posted February 1, 2013 Q:A tennis ball is served horizontally from 2.4m above the ground at 30m/s (a)The net is 12m away and 0.9m high, will the ball clear the net? (b)Where will the ball land? :sorrow: Quote Link to comment Share on other sites More sharing options...

0 HibaSyed Posted February 1, 2013 Author Share Posted February 1, 2013 Data: V_{0}x= 30m/s H_{1}= 2.4 m V_{0}y= 0 X= 12m H_{2}= 0.9m To find: (a) Will the ball clear the net? ( X’= ? Solution: (a) X= V_{0}x t 12=30 t 12/30 = t t= 0.4 s As, H=V_{0}y t + ½ g t^{2} H= (0)(0.4)+1/2(-9.8)(0.4)^{2} H= -0.78m -ve sign shows that the height of the ball at the net from the top. Height of the ball at the net and from the ground= H_{1}-H=2.4-0.78=1.62m As 1.62m>0.9m so the ball will clear the net. ( H_{1}= V_{0}y t’ + ½ g t’^{2} -2.4= (0)t’ + ½ (-9.8) t’^{2} . . . t’= 0.69s X’=V_{0}x t’ X’=(30)(0.96) X’= 20.7m This is the solution my teacher came up with and honestly I have no idea whats going on? :/ Quote Link to comment Share on other sites More sharing options...

0 HibaSyed Posted February 1, 2013 Author Share Posted February 1, 2013 How can the height be -ve!? :/ It doesn't make sense... Quote Link to comment Share on other sites More sharing options...

0 FizziksGuy Posted February 4, 2013 Share Posted February 4, 2013 The negative sign on the height just indicates that the ball is lower than when it started. Your teacher is calling the launch height 0, and determining when the ball crosses the net it has fallen that amount vertically. Check out our projectile motion tutorials/videos as a starting point and see if that helps. If not, if you can give us an idea of what you're thinking, what you've figured out so far, and where you're stuck, it will make providing assistance much more straightforward. Good luck! Projectile Motion Video Projectile Motion Tutorials Quote Link to comment Share on other sites More sharing options...

0 Thai Pham Posted February 23, 2013 Share Posted February 23, 2013 Q:A tennis ball is served horizontally from 2.4m above the ground at 30m/s (a)The net is 12m away and 0.9m high, will the ball clear the net? (b)Where will the ball land? :sorrow: This is a very good question and I got the same answer as your teacher :eagerness: The first thing I should do is drawing the diagram to see the actual picture of the problem Next, since this is Projectile Motion problem, this problem require 2 components, x and y Now, no the given, so you can choose which equation to choose. For this, we choose the following equation [TABLE="class: maths"] [TR] [TD="align: right"]x = [/TD] [TD="align: left"]x_{0} + v_{0}Δt + ½aΔt^{2}^{}^{}[/TD] [/TR] [/TABLE] Now, set the two components for x and y y-component: Y_{f} - Y_{i} = V_{(iy) }t + 12 a_{y}t^{2}^{}You know the origin is where the ball is hit which makes yf=0 and yi which stand for y final equal to -2.4m. v initial is zero because the ball is throwing side away so imagine like dropping the ball. The acceleration is 9.8. Now sub it in, you get the amount of time that it takes to hit the ground. x-component: v initial is 30m/s acceleration is 0 since the direction is going side way just plug it in to the x component. After you have the equation set up, plug in the t which give you the answer for B. The distance that it hits the ground For part A just use 12m away, so you want to know when the ball flies pass at 12m. Simple, use the x component equation. make x-xinitial=12m. Now you have the time which is 0.4second The last step is plug into y component to find how high was the ball almost reach to the ground which is 0.784m Now you can get the answer by simply take 2.4m-0.784m=20.7m I hope this help, if you have trouble doing this, should check out more videos tutorials :star: Quote Link to comment Share on other sites More sharing options...

0 FizziksGuy Posted February 25, 2013 Share Posted February 25, 2013 Thanks for helping out our forum members! Quote Link to comment Share on other sites More sharing options...

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## HibaSyed

Q:A tennis ball is served horizontally from 2.4m above the ground at 30m/s

(a)The net is 12m away and 0.9m high, will the ball clear the net?

(b)Where will the ball land?

:sorrow:

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