Answer:
a) -4 N
b) +4 N
Explanation:
Draw a free body diagram for each block.
For the large block, there are 2 forces: 12 N pushing to the right, and F pushing to the left.
For the small block, there is 1 force, F pushing to the right.
There are also weight and normal forces in the vertical direction, but we can ignore those.
Sum of forces on the large block in the x direction:
∑F = ma
12 − F = 4a
Sum of forces on the small block in the x direction:
∑F = ma
F = 2a
2F = 4a
Substitute:
12 − F = 2F
12 = 3F
F = 4
The small block pushes on the large block 4 N to the left (-4 N).
The large block pushes on the small block 4 N to the right (+4 N).
Answer:
1. Unit for work is measured in Joules.
Formula for work is power * time taken
2 The unit for force is Newton
A work done in lifting a jar of water
3. The unit for measuring power is Joules.
The formula for measuring power is work done/time taken
Answer:
A. F=6.65*10^{-10}N
B. south - north
Explanation:
A) We use the Lorentz force
F = qv X B
|F| = qvB
to calculate the magnitude of the force we need the speed of the of the ball.

and by replacing in the formula for the magnitude of the force we have (taking into account the excess of electrons)

B)
b. south - north (by the rigth hand rule)
I hope this is usefull for you
regards