Physics Help Forum "Win the Prize" Projectile motion

 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

 Sep 14th 2010, 11:43 PM #1 Junior Member   Join Date: Sep 2010 Posts: 8 "Win the Prize" Projectile motion Hello all, I have worked through this problem several different ways, and cannot get my answer to match that of the book's. The attached picture is my work thus far, if you could, please point out any mistakes or hints as to where I must go with my arithmetic. Thank you, CC Attached Thumbnails
 Sep 14th 2010, 11:48 PM #2 Junior Member   Join Date: Sep 2010 Posts: 8 Also, please ignore the random 1.29m/s in the middle of the graph. I forgot to post the question as well. Here it is: In a carnival booth, you win a stuffed giraffe if you toss a quarter into a small dish. The dish is on a shelf about the point where the quarter leaves your hand and is a horizontal distance of 2.1m from this point. If you toss the coin with a velocity of 6.4m/s at an angle of 60(degrees) above the horizontal, the coin lands in the dish. You can ignore air resistance. (a) what is the height of the shelf above the point where the quarter leaves your hand? (b) What is the vertical component of the velocity of the quarter just before it lands in the dish?
 Sep 14th 2010, 11:56 PM #3 Junior Member   Join Date: Sep 2010 Posts: 8 Here is the picture that the book provides. Attached Thumbnails
 Sep 15th 2010, 08:16 AM #4 Physics Team     Join Date: Jun 2010 Location: Naperville, IL USA Posts: 2,271 Here's how to proceed: 1. The time of the flight is D_x/v_x, where D_x = horizontal distance traveled = 2.1m, and v_x = horiz velocity = 6.4 m/s cos(60) = 3.2 m/s. Hence t = 2.1m/(3.2m/s) = 0.66s 2. The vertical position of the coin at t=0.66s is: y = ut + 1/2 at^2 = 6.4m/s sin(60) 0.66s - 1/2(9.8 m/s^2)(0.66s)^2 = 3.64m The vertical velocity at t= 0.66s is: v = u + at = 6.4m/s sin(60) - 9.8m/s^2 (0.66s) = -0.89m/s
 Sep 15th 2010, 09:30 AM #5 Junior Member   Join Date: Sep 2010 Posts: 8 Thank you very much, I found out where I goofed! It is much appreciated
 Sep 15th 2010, 09:36 AM #6 Physics Team     Join Date: Jun 2010 Location: Naperville, IL USA Posts: 2,271 So - what prize do I win????
 Sep 15th 2010, 09:53 AM #7 Junior Member   Join Date: Sep 2010 Posts: 8 A thanks!
Sep 15th 2010, 05:02 PM   #8
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 Originally Posted by ChipB v = u + at = 6.4m/s sin(60) - 9.8m/s^2 (0.66s) = -0.89m/s
Hello again, I was trying to find the Vy at .66s like you do shown in the quote above. When I do the calculation myself I get around -.93m/s

Also, will you explain what you did there?

What I see is this:

Vy-at

Where did you derive that equation from?

Sorry for all of the questions, I am just trying to see where I am missing something.

Thanks,
CC

 Sep 15th 2010, 07:00 PM #9 Physics Team     Join Date: Jun 2010 Location: Naperville, IL USA Posts: 2,271 I think the difference between your answer and mine is I used t = 2.1m/(6.4 m/s x cos(60)) = 2.1/3.2 = 0.65625s , and you may have rounded this to 0.66s. v(t= 0.656s) = 6.4 sin(60) - (9.8)(0.656) = -0.89m/s This equation comes from: v = u +at where u = initial velocity and a = acceleration. Here a = -g = -09.8 m/s^2.
Dec 30th 2017, 02:48 AM   #10
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Posts: 1
 Originally Posted by CalculusCrazed Here is the picture that the book provides.
please may i know the name of the book

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# a carnival booth, you win a stuffed giraffe if you

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