Lets drive to physics
If flat car is given an acceleration a = 3 ms − 2 starting from rest, compute tension (in N ) in the light inextensible string connected to block A of mass 3 0 kg . Coefficient of friction between block and flat car is μ = 0 . 5 0 .
Neglect mass of pulley and its friction. Take g = 1 0 ms − 2 .
The answer is 330.
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2 solutions
@Abhishek Sharma @Purushottam Abhisheikh .Is there a effect because block is kept on the the Truck? Will there be a change in answer if the block is kept on the ground And the pulley(attached to the truck) is moving with acceleration a. @Kushal Patankar .
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Either you put block on the truck or on the ground the result will be same till the pulley moves with acceleration a and one end of the string is fixed.
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@Purushottam Abhisheikh , If the block is kept on the the truck then won't it tend to go backward with the acceleration a and if kept on the ground this pseudoforce or the tending nature of the block will not be there. And this should have some effect.Correct me if I am wrong.
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@A Former Brilliant Member – In both cases pseudo force will have same value as it is nothing but the force on block felt by the observer which is on the truck.
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@Purushottam Abhisheikh – Thanks! Now I get my mistake .Messing with pseudo force and all.
Had some doubts in my mind regarding acceleration of the block. My first attempt went wrong but then the 2a acceleration came into my mind :)
Solution_Upvoted
Agh, I accidentally thought the block had acceleration a . Evidently I'm not very good at Physics :P
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But you are very good at maths so dont bother about it.
Try this constraint question Here
I still do not quite get why you used 2a instead of a. Could you help me one this one?
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Use ∑ T . a = 0 . I hope this will help you.
I think there should be pseudo force considered because there is not only friction taking place due to the motion of cart . We can explain it by the concept of pseudo force .
As when we see from the ground we notice that it is accelerating with 2a+a (of cart)= 3a
And when we stand on the cart we notice the block's acceleration to be 2a
Thus we know that it is accelerating with 3a but we see that it is acc with 2a
Therefore we should pseudo force in backward direction to study this motion
Nevertheless I will consult my teacher about this doubt .
Wh should the block have acceleration 2 a ? Can someone please explain?
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Use ∑ T . a = 0 . I hope this will help you.
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i cant get you ...........will you please elaborate?????
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@Debabrata Mukherjee – As the string is massless and inextensible it can not store any type of energy within itself. Hence ∑ T . x = 0 (where x is displacement of point or points at which tension is acting). Differentiate it w.r.t. time twice and you will get the required result.
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@Purushottam Abhisheikh – now i got it....really thank you!!!!!!!!!
If we solve this ques. using pseudo force. The pseudo force acting on the block is 90N and max friction is 150N. Hence,block will not move and therefore there will be no tension in the rope.Please guide me where i am wrong. Thanks
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I think that since the car is accelerating forward hence the length of fixed part of pulley would increase and hence block will accelerate forward with an acceleration 2a wrt ground frame and not car frame so pseudo force is not taken.
If you solve from car frame then the block will accelerate with an acceleration 'a' wrt car and pseudo force can be applied. T-(90)-150=(30)(a) , On putting a = 3, we get T=330N.
Yeah I know. But it is still in level 4.
If the flatcar has acceleration a then block A will have acceleration 2 a .
Applying newton's second law of motion,
T − μ m g = 2 m a .
Putting the values we get,
T = 3 3 0 N