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Mechanics January 2007 Watch

1. Could someone help me with january 2007 M1 , Question 7f.

Why does the string become taught again once the particle goes up the plane and then back down to its original position.

http://www.mathspapers.co.uk/edexcel.html
2. (Original post by thelion0)
Could someone help me with january 2007 M1 , Question 7f.

Why does the string become taught again once the particle goes up the plane and then back down to its original position.

http://www.mathspapers.co.uk/edexcel.html
The string is taught while the weight Q is pulling P up the slope.
It is taught at the instant Q hits the ground and then become slack as P continues to move up the slope, stops and then falls back down the slope under gravity. The string becomes taught again when P returns to the point where it was when Q hit the ground.
3. When Q touches the ground, Q will no longer be accelerating (it can't go into the ground). So Q will no longer be "pulling" the string. So the string will not be taught and the tension will go to 0. Then P will start accelerating down the plane (due to it's vertical weight component), and will start pulling the string. After a particular time, P will pull the string tight again. 7f) is asking you to find this time.

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