Help and explain please

a) Moment = 200N.m

              b) F = 500N

Explanation: Moment or Torque is the tendency of a body to rotate because of an aplplied force. It can be calculated as

F is force applied

r is distance from the force to the point of rotation

θ is the angle formed between force and distance

a) Since F and r are perpendicular, θ=90°, sin90° = 1, so

200

Torque caused by weight of the barrier at the pivot is 200N.m

b) Counterweight has the same torque as pivot: 200

So, to find Force necessary to balance the weight:

F = 500

It is necessary a force of 500N from the counterweight to balance the weight.

c) up is the direction the magnetic force is acting on the charge.

heats surface water up