If you cannot get a chair to move across the floor, it is because static friction opposes your push. When you say static or kinetic friction the two object that facing each other are opposing each other. That's why you're having a hard time pushing the chair.
Four of them pass a point every second.
The number converted is 
Explanation:
In order to convert from the original units to the final units, we have to keep in mind the following conversion factors:



The original unit that we have is

Therefore, it can be rewritten as:

Therefore, since the initial number was 0.779, the final value is

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Answer:
40 N
Explanation:
We are given that
Speed of system is constant
Therefore, acceleration=a=0
Tension applied on block B=T=50 N
Friction force=f=10 N
We have to find the friction force acting on block A.
Let T' be the tension in string connecting block A and block B and friction force on block A be f'.
For Block B

Where
=Mass of block B
Substitute the values


For block A

Where
Mass of block A
Substitute the values


Hence, the friction force acting on block A=40 N
Answer:B.
Both increase as the mass and velocity increase.