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 May 12th 2014, 09:20 AM #1 Junior Member   Join Date: May 2014 Posts: 2 Solve this question??????? http://physicshelpforum.com/attachme...1&d=1399911403 Please tell me the correct answers of all the three parts...
 May 12th 2014, 10:30 AM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,347 We're not going to just give you the answers to your homework, but we will help you work through them. So let's start - the first question is asking what the initial velocity of the ball must be for it to rise to a height of 20m before falling back down. This uses one of the equations of motion with which you should be familiar: v_f^2 - v_i^2 = 2ad Here v_f (final velocity) is 0 when the ball reaches its apex, v_i is the initial velocity which you are trying to determine, 'a is acceleration, which they say is -10 m/s^2, an d = 20 m. Solve for v_i. To do the next two problems you first need to determine the time it takes for the ball to reach its highest point. For that you can use v_f = v_1 + at, where again v_f = 0, v_i you just determined in part 1, and a = -10 m/s^2. Solve for t. Now that you have time t you can determine how far the plane traveled using the equation of motion for the plane: d= v_it + (1/2) at^2, where you are told that v_i = 0 and a = 2m/s^2. For part 3 use a similar technique to find the distance the plane travels as the ball falls, and use Pythagoras to find the distance between the man and the plane.
May 12th 2014, 10:33 PM   #3
Junior Member

Join Date: May 2014
Posts: 2
 Originally Posted by ChipB We're not going to just give you the answers to your homework, but we will help you work through them. So let's start - the first question is asking what the initial velocity of the ball must be for it to rise to a height of 20m before falling back down. This uses one of the equations of motion with which you should be familiar: v_f^2 - v_i^2 = 2ad Here v_f (final velocity) is 0 when the ball reaches its apex, v_i is the initial velocity which you are trying to determine, 'a is acceleration, which they say is -10 m/s^2, an d = 20 m. Solve for v_i. To do the next two problems you first need to determine the time it takes for the ball to reach its highest point. For that you can use v_f = v_1 + at, where again v_f = 0, v_i you just determined in part 1, and a = -10 m/s^2. Solve for t. Now that you have time t you can determine how far the plane traveled using the equation of motion for the plane: d= v_it + (1/2) at^2, where you are told that v_i = 0 and a = 2m/s^2. For part 3 use a similar technique to find the distance the plane travels as the ball falls, and use Pythagoras to find the distance between the man and the plane.
Thnx for the reply....i ve got it

But mine answer of third part is "26.5m" but mine friend's answer is "23.3m" so plz tell me correct answer of 3rd part.

 May 13th 2014, 04:33 AM #4 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,347 Neither - I get 25.6m. What distance did you calculate that the plane has moved past the man (i.e. the horizontal leg of the right triangle)?

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