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# Mechanics in maths watch

1. A particle A, of mass 0.8kg, resting on a smooth horizontal table, is connected to a particle B, of mass 0.6kg which is 1m from the ground, by a light inextensible string passing over a small smooth pulley at the edge of the table. The partivle A is more than 1m from the edge of the table. The system is released from rest with the horizontal part of the stringperpendicular to the edge of the table, the hanging parts vertical and the string taut.
a) Calculate the acceleration of A
b) the tension of the string
c) the speed of B when it hits the ground
d) the time taken for B to reach the ground
2. (Original post by Apples13)
A particle A, of mass 0.8kg, resting on a smooth horizontal table, is connected to a particle B, of mass 0.6kg which is 1m from the ground, by a light inextensible string passing over a small smooth pulley at the edge of the table. The partivle A is more than 1m from the edge of the table. The system is released from rest with the horizontal part of the stringperpendicular to the edge of the table, the hanging parts vertical and the string taut.
a) Calculate the acceleration of A
b) the tension of the string
c) the speed of B when it hits the ground
d) the time taken for B to reach the ground
What have you done so far? Try drawing force diagrams for each particle. Remember that because the string is inextensible, the tension in the string will be the same for both particles - just make sure you get it acting in the right direction.
3. (Original post by TheMindGarage)
What have you done so far? Try drawing force diagrams for each particle. Remember that because the string is inextensible, the tension in the string will be the same for both particles - just make sure you get it acting in the right direction.
I have drawn a diagram and for a) i thinj ive got to use f=ma but im not sure what value to use for f
4. initially the only external force acting on the system is the weight of B downwards.

this net force has to accelerate both masses ie 1.4kg

you should be able to find the acceleration of B downwards ( and A which is the same but horizontal )
5. (Original post by Apples13)
I have drawn a diagram and for a) i thinj ive got to use f=ma but im not sure what value to use for f
f is the resultant force. It should be the weight minus the tension from the string (remember to consider direction).

Do the same thing with B as well. Then set the accelerations equal to each other (being extremely careful with the direction of the forces and accelerations).
6. (Original post by TheMindGarage)
f is the resultant force. It should be the weight minus the tension from the string (remember to consider direction).

Do the same thing with B as well. Then set the accelerations equal to each other (being extremely careful with the direction of the forces and accelerations).
How do i work out the tension of the string?
7. (Original post by Apples13)
How do i work out the tension of the string?
By forming equations. You know that the tension and acceleration are the same throughout. Form expressions for the resultant force for each particle and then for acceleration. Then equate them.

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