The force exerted by a magnetic field on a wire carrying current is:

where I is the current, L the length of the wire, B the magnetic field intensity, and

the angle between the wire and the direction of B.
In our problem, the force is F=0.20 N. The current is I=1.40 A, while the length of the wire is L=35.0 cm=0.35 m. The angle between the wire and the magnetic field is

, so we can re-arrange the formula and substitute the numbers to find B:
Position and momentum.
This is Heisenberg's Uncertainty Principle:
Δx Δp ≥ h ÷ 4π, where Δx is the change in position, Δp is the change in momentum, and h is Planck's Constant.
Answer:
Frictional force, F = 45.9 N
Explanation:
It is given that,
Weight of the box, W = 150 N
Acceleration, 
The coefficient of static friction between the box and the wagon's surface is 0.6 and the coefficient of kinetic friction is 0.4.
It is mentioned that the box does not move relative to the wagon. The force of friction is equal to the applied force. Let a is the acceleration. So,



Frictional force is given by :


F = 45.9 N
So, the friction force on this box is closest to 45.9 N. Hence, this is the required solution.