MECHANICS urgent help needed Watch

Kercmaher
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#1
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The height of a tennis ball above the ground can be modelled using the equation

h=1.7+0.18x-0.01x^2

h is the height above the ground and x is the horizontal distance above the ground

To be called in the tennis ball must hit theground before it travels a horizontal distance of 25m

Will the tennis ball be called in??

Please help i have no idea what to use... suvat formulas or what?
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RickHendricks
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(Original post by Kercmaher)
The height of a tennis ball above the ground can be modelled using the equation

h=1.7+0.18x-0.01x^2

h is the height above the ground and x is the horizontal distance above the ground

To be called in the tennis ball must hit theground before it travels a horizontal distance of 25m

Will the tennis ball be called in??

Please help i have no idea what to use... suvat formulas or what?
draw the graph of h on the y-axis and x on the x-axis (or sketch)

See whether the value of h is before 25 or after 25.
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Kercmaher
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(Original post by RickHendricks)
draw the graph of h on the y-axis and x on the x-axis (or sketch)

See whether the value of h is before 25 or after 25.
ive done this but it doesnt really help me.. is there no other way? Thank you
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RickHendricks
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(Original post by Kercmaher)
ive done this but it doesnt really help me.. is there no other way? Thank you
take h as y and x as just x.

write y in terms of x

let y=0
solve it.
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stephen1011
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(Original post by Kercmaher)
The height of a tennis ball above the ground can be modelled using the equation

h=1.7+0.18x-0.01x^2

h is the height above the ground and x is the horizontal distance above the ground

To be called in the tennis ball must hit theground before it travels a horizontal distance of 25m

Will the tennis ball be called in??

Please help i have no idea what to use... suvat formulas or what?
https://s9.postimg.cc/w1j3uguhr/1526...3016579182.jpg
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Prasiortle
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(Original post by Kercmaher)
ive done this but it doesnt really help me.. is there no other way? Thank you
You're not reading the information that's right in front of you. h is the height above the ground, so "on the ground" is represented by h=0. So where does the ball hit the ground? It hits the ground when h=0, ime. 1.7+0.18x-0.01x^2 = 0. You should know how to solve using the quadratic formula. Now, you'll have found values for x, but what does x represent? Read actively and look back at the question - x is the horizontal distance, which clearly can't be negative, so you'll need to discard one of the roots the quadratic formula gives you, and select the other one. Now, the question is "will the ball be called in?" Well, the ball gets called if it hits the ground before travelling a horizontal distance of 25, i.e. at the point when it hits the ground, the horizontal distance is less than 25. You've just found the horizontal distance, so all you have to do now is compare it to 25 to determine whether the answer is "Yes" or "No".
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libbybibster
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I just spent ages doing this question before i realised i was being an idiot. If you use a graphical calculator with the equation solver make sure you put the coefficients in the right places considering the x^2 term is last
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the bear
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so just solve the quadratic equation

-0.01x2 + 0.18x + 1.7 = 0
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ghostwalker
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Question is 9 mths old.
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