Answer :
.
Explanation:
It is given that,
Electric field strength, 
We know that,
Charge of electron, 
Mass of electron, 
From the definition of electric field,
...............(1)
According to Newton's second law, F = ma..........(2)
From equation (1) and (2)




or

So, the horizontal component of acceleration of an electron is
.
Hence, it is the required solution.
Answer:
(a) Magnitude of static friction force is 109 N
(b) Minimum possible value of static friction is 0.356
Solution:
As per the question;
Horizontal force exerted by the girl, F = 109 N
Mass of the crate, m = 31.2 kg
Now,
(a) To calculate the magnitude of static friction force:
Since, the crate is at rest, the forces on the crate are balanced and thus the horizontal force is equal to the frictional force, f:
F = f = 109 N
(b) The maximum possible force of friction between the floor and the crate is given by:

where
N = Normal reaction = mg
Thus

For the crate to remain at rest, The force exerted on the crate must be less than or equal to the maximum force of friction.




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