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Two similar wooden blocks are tied one behind the other and pulled across a level surface. Friction is not negligible. The force required to pull them at constant speed is F. If one block is stacked upon the other then the new force required to pull them at constant speed will be approximately

Two similar wooden blocks are tied one behind the other and pulled across a level surface. Friction is not negligible. The force required to pull them at constant speed is F. If one block is stacked upon the other then the new force required to pull them at constant speed will be approximately

Grade:upto college level

1 Answers

Deepak Patra
askIITians Faculty 471 Points
9 years ago
The correct option is:
(B) F.
The free body diagram for block 1 (tied to block 2 via string) is.
233-2293_18.PNG
The blocks move with constant speed, therefore the net force acting on the blocks must be zero. to account for same, substitute the net force on each block with zero as:
F – ƒk – T = 0
Here, ƒk is the force of kinetic friction between block and the surface, and T is the tension in the string.
The free body diagram of block 2 is:
233-669_19.PNG
The net force on block 2 is written as:
T – ƒk = 0
T = ƒk
Substitute T = ƒk in equation F – ƒk – T = 0,
233-1246_20.PNG
The kinetic force of friction is also given as:
233-2316_21.PNG
When the blocks stack upon each other, the force of friction experienced by the block is:
233-1420_22.PNG

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