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M2 question help

hi I'm struggling with this M2 question

question 3b ii. also 3b iii

http://www.mei.org.uk/files/papers/m206ju_rw67.pdf


i am unsure how to approach the question
any help would be appreciated

thanks
(edited 12 years ago)
Reply 1
At first glance, use the equations of motion.
You want the initial velocity, you can calculate the acceleration and you are given the end velocity (instantaneously at rest) and a form of distance.

However, after looking again, you are given information about energy so you would probably want to use the potential energy and kinetic energy of the box. This way should be a lot quicker to get the answer.
(edited 12 years ago)
Reply 2
Original post by Akryn
At first glance, use the equations of motion.
You want the initial velocity, you can calculate the acceleration and you are given the end velocity (instantaneously at rest) and a form of distance.

However, after looking again, you are given information about energy so you would probably want to use the potential energy and kinetic energy of the box. This way should be a lot quicker to get the answer.



ok i see. i understand the suvat equations but how would i go about calculating the acceleration?
Reply 3
Original post by johnkean
ok i see. i understand the suvat equations but how would i go about calculating the acceleration?


By using the frictional and weight forces.
Reply 4
Original post by johnkean
hi I'm struggling with this M2 question

question 3b ii. also 3b iii

http://www.mei.org.uk/files/papers/m206ju_rw67.pdf


i am unsure how to approach the question
any help would be appreciated

thanks


Here is how you will do 3b(ii),
Use the work energy principle, for this part it will be:
loss in KE = gain in PE + work done against friction + work done against air resistance

Just insert the values into the upper equation and you will be able to find v, the initial speed.
For loss in KE, insert 0.5*11*v*v
Remember that in PE you need to insert the height, the vertical component. Just let the angle between the slope and the horizontal be 'x'. So PE should be 11*9.8*1.5sinx
Work done against friction will be: 1.5*ur = 1.5 * 0.2 * R
Work done against air resistance will be: 6*1.5 =9
Just solve it, according to my calculation you should get v=4.29m/s

Here is how you will do the next part:
Again use work energy principle, this time it will look like this:
loss of PE = gain in KE + work done against friction + work done against air resistance
KE will equal to 0.5*11*v*v Remember that v will be found in the previous part.
Let the distance PQ be 'z'. So you can write the height in PE equation as (1.5+z)sinx.
Work done against friction will be (1.5+z)uR
Work done against air resistance will be 6*(1.5+z)
Solve the equation and find 'z' this is the distance PQ.
I got the answer as 4.99m

NB: I have just roughly solved it, so my answers may not be accurate but the method is correct.
Reply 5
Original post by raheem94
Here is how you will do 3b(ii),
Use the work energy principle, for this part it will be:
loss in KE = gain in PE + work done against friction + work done against air resistance

Just insert the values into the upper equation and you will be able to find v, the initial speed.
For loss in KE, insert 0.5*11*v*v
Remember that in PE you need to insert the height, the vertical component. Just let the angle between the slope and the horizontal be 'x'. So PE should be 11*9.8*1.5sinx
Work done against friction will be: 1.5*ur = 1.5 * 0.2 * R
Work done against air resistance will be: 6*1.5 =9
Just solve it, according to my calculation you should get v=4.29m/s

Here is how you will do the next part:
Again use work energy principle, this time it will look like this:
loss of PE = gain in KE + work done against friction + work done against air resistance
KE will equal to 0.5*11*v*v Remember that v will be found in the previous part.
Let the distance PQ be 'z'. So you can write the height in PE equation as (1.5+z)sinx.
Work done against friction will be (1.5+z)uR
Work done against air resistance will be 6*(1.5+z)
Solve the equation and find 'z' this is the distance PQ.
I got the answer as 4.99m

NB: I have just roughly solved it, so my answers may not be accurate but the method is correct.



brilliant, thanks a lot. exactly what i was looking for

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