A block, kept on ground, requires 10 N of horizontal force to just start moving. If we apply a force of 5 N on the block in horizontal direction, what will be the magnitude of frictional force acting on it?

Q. Two blocks, with masses

m_{1}

and

m_{2}

, are stacked as shown in Fig. and placed on a frictionless horizontal surface. There is a friction between two blocks. An external force applied to the top block at an angle

α

below the horizontal.
a. If the two blocks move together, find their acceleration.
b. Calculate the maximum value of force so that blocks will move together.

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A 10.0kg block is stacked on top of the 8kg block. What is the magnitude F of the force, acting horizontally on the 8kg block as before, that is required to make the two blocks start to move?

The correct option is C 45NCoefficient of static friction μs=0.255 (solved earlier)Now a 10.0kg block is placed at the top of 8.0kg block.Total force required to just move both blocks F=μsMgwhere M=10+8=18kg∴ F=0.255×18×9.8=45N

A $10.0 k g$ block is stacked on top of the $8 k g$ block. What is the magnitude F of the force, acting horizontally on the $8 k g$ block as before, that is required to make the two blocks start to move?

The correct option is C $45 N$
Coefficient of static friction $μ_{s} = 0.255$ (solved earlier)
Now a $10.0 k g$ block is placed at the top of $8.0 k g$ block.
Total force required to just move both blocks $F = μ_{s} M g$
where $M = 10 + 8 = 18 k g$
$∴$ $F = 0.255 \times 18 \times 9.8 = 45 N$