# Help with Mechanics AQA A-Level question?

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#1
Im struggling with part b of Q 18 of the AQA 2021 Mechanics resources, plus they don't have a markscheme so I have no idea if im doing anything wrong or right
Block a of mass 0.2kg lies at rest on a rough plane.

The plane is inclined at an angle θ to the horizontal, such that tanθ= 7/24.

A light inextensible string is attached to A and runs parallel to the line of greatest slope until it passes over a smooth fixed pulley at the top of the slope.

The other end of the string is attached to particle B, of mass 2 kg, which is held at rest so that the string is taut, as shown in the diagram.

A) B is released from rest so that it begins to move vertically downwards with an acceleration of 543/625ms^-2. Show that the coefficient of friction between A and the inclined plane is 0.17. (8 marks)

(I did this part a) fine and got the 0.17)

b)i) When A reaches 0.5ms-1, the string breaks.
Find the distance travelled by A after the string breaks until first coming to rest. Take g to be 9.81ms-2

(I'm assuming Suvat? s is what you want to find, u being initial velocity which should be 0.5ms-1, since that's what it is when it breaks, v to be 0 and a to be 9.81, then use v^2=u^2+2as, to find s? Im really not sure though)

b)ii) State an assumption which could affect the validity of your answer to b)I)
(assuming anything like there isn't any other resistant forces etc acting on it, air resistance etc)

any help is much appreciated!
Last edited by studentinneed17; 1 year ago
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1 year ago
#2
(Original post by studentinneed17)
b)i) When A reaches 0.5ms-1, the string breaks.
Find the distance travelled by A after the string breaks until first coming to rest. Take g to be 9.81ms-2

(I'm assuming Suvat? s is what you want to find, u being initial velocity which should be 0.5ms-1, since that's what it is when it breaks, v to be 0 and a to be 9.81, then use v^2=u^2+2as, to find s? Im really not sure though)
b)i) A block on an inclined plane is not going to have an acceleration of g, or -g.

Since the string has gone slack, you can treat in the standard manner for a block on an inclined plane with friction.
Last edited by ghostwalker; 1 year ago
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