Author Topic: Mechanics Question  (Read 6784 times)

Offline S.M.A.T

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Re: Mechanics Question
« Reply #30 on: October 17, 2010, 02:48:12 am »
A ball is projected from a point O on the edge of a vertical cliff. The horizontal and vertically upward components of the initial velocity are 7ms-1 and 21ms-1 respectively. At the time t seconds after the projection the ball is at the point (x,y) referred to horizontal and vertically upward axes through O. Air resistance may be neglected.

(i) Express x and y in terms of t, and hence show that y= 3x- 0.1x2

The ball hits the sea at a point which is 25m below the level of O.

(ii) Find the horizontal distance between the cliff and the point where the ball hits the sea.

(i)  x=7t(horizontal velocity always remain  constant so the formula used is s=vt)
      y=21t-0.5gt2(s=ut+0.5at2)
    
      t=(x/7)
        
      y=21t-0.5gt2
      y=21(x/7) -0.5g(x/7) 2
      y=3x-0.1x2
(ii) y=-25(because the question said y is vertically upward axes through O the ball hits below O so negative 25)
     3x-0.1x2=-25
    0.1x2-3x-25=0
    solving this equation we get
     x=36.8m

   
« Last Edit: October 17, 2010, 02:58:30 am by asiftasfiq93 »


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Offline Arthur Bon Zavi

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Re: Mechanics Question
« Reply #31 on: October 17, 2010, 07:25:34 am »
(i)  x=7t(horizontal velocity always remain  constant so the formula used is s=vt)
      y=21t-0.5gt2(s=ut+0.5at2)
    
      t=(x/7)
        
      y=21t-0.5gt2
      y=21(x/7) -0.5g(x/7) 2
      y=3x-0.1x2
(ii) y=-25(because the question said y is vertically upward axes through O the ball hits below O so negative 25)
     3x-0.1x2=-25
    0.1x2-3x-25=0
    solving this equation we get
     x=36.8m

   


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Offline S.M.A.T

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Re: Mechanics Question
« Reply #32 on: October 18, 2010, 10:55:13 am »
Have You Completed yous A Levels? :D

no,still doing my A2.:)


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Offline Arthur Bon Zavi

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Re: Mechanics Question
« Reply #33 on: October 18, 2010, 01:22:20 pm »
no,still doing my A2.:)

Well Then Go Ahead!  8)

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Offline astarmathsandphysics

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Re: Mechanics Question
« Reply #34 on: October 20, 2010, 09:03:36 am »
they found the angle between south and the 6N force and resolved vertically

Offline Ghost Of Highbury

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Re: Mechanics Question
« Reply #35 on: October 20, 2010, 01:24:08 pm »
attached



Can u help with the second subpart too plz?

Y do they use F = T cos (sin-1 0.6)
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Re: Mechanics Question
« Reply #36 on: October 20, 2010, 02:07:43 pm »
Can u help with the second subpart too plz?

Y do they use F = T cos (sin-1 0.6)

What question are you referring to ?

Offline Ghost Of Highbury

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Re: Mechanics Question
« Reply #37 on: October 20, 2010, 02:20:45 pm »
iVE quoted it.

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elemis

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Re: Mechanics Question
« Reply #38 on: October 20, 2010, 03:02:26 pm »
iVE quoted it.



But whats the ORIGINAL question ? All you've quoted is the answers Nid gave you - I cant find your question anywhere.

Offline Ghost Of Highbury

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Re: Mechanics Question
« Reply #39 on: October 20, 2010, 03:27:40 pm »
But whats the ORIGINAL question ? All you've quoted is the answers Nid gave you - I cant find your question anywhere.

Click on the "Quote from...." mate.
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Offline Ghost Of Highbury

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Re: Mechanics Question
« Reply #40 on: October 20, 2010, 03:33:03 pm »
I know that the Friction force is stopping the ring to slip and opposing T too.

I think it should be F = T + Wsin53.1 (weight component)

But the answer seems to ignore the W, and instead give the equation F = Tsin53.1
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elemis

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Re: Mechanics Question
« Reply #41 on: October 20, 2010, 03:41:24 pm »
Click on the "Quote from...." mate.

I did that. I'm not dumb you know.... :P

I figured out you were talking about Dania's question.

This whole time I was looking for a question posted by YOU.


Offline Ghost Of Highbury

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Re: Mechanics Question
« Reply #42 on: October 20, 2010, 03:56:38 pm »
I did that. I'm not dumb you know.... :P

I figured out you were talking about Dania's question.

This whole time I was looking for a question posted by YOU.



Ahh ok.
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Offline Deadly_king

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Re: Mechanics Question
« Reply #43 on: October 20, 2010, 04:29:29 pm »
I know that the Friction force is stopping the ring to slip and opposing T too.

I think it should be F = T + Wsin53.1 (weight component)

But the answer seems to ignore the W, and instead give the equation F = Tsin53.1

W acts perpendicular to the ring...............hence it has no component!

Offline Ghost Of Highbury

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Re: Mechanics Question
« Reply #44 on: October 20, 2010, 05:21:32 pm »
W acts perpendicular to the ring...............hence it has no component!

Could you elaborate that plz, and sry for the trouble.
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