Answer:
Explanation:
Given
charge is placed at 
another charge of
is at 
We know that Electric field due to positive charge is away from it and Electric field due to negative charge is towards it.
so net electric field is zero somewhere beyond negatively charged particle
Electric Field due to
at some distance r from it

Now Electric Field due to
is

Now 



thus 
Thus Electric field is zero at some distance r=1.43 cm right of
Answer:
Final length= 746.175 mm
Explanation:
Given that Length of aluminium at 223 C is 750 mm.As we know that when temperature of material increases or decreases then dimensions of material also increases or decreases respectively with temperature.
Here temperature of aluminium decreases so the final length of aluminium decreases .
As we know that

Now by putting the values

ΔL=3.82 mm
So final length =750-3.82 mm
Final length= 746.175 mm