Friction is a force that always acts a) perpendicular to an objects motion b) opposite to an objects motion c) in a the same direction as the objects motion

B) opposite to objects motion.

Explanation:

Friction is a force that always acts opposite to an objects motion. Frictional force is a force of opposition that acts in the opposite direction to the direction of force creating motion(moving force).

This frictional force always is equal to the moving force for a static body (body not accelerating) but less than the moving force for an accelerating object.

When the body is accelerating, the force of friction will not be able to overcome the moving force any longer.

For example, if a block is dragged on an horizontal floor using a force of 5N(moving force), the frictional force will also be 5N since it is a force of opposition acting in the opposite direction to the moving force. This is only true for static body.

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.

electrical potential energy =0.072 j

explanation:

electrical potential energy is given by

u= q δv

q= charge=6 c

δv= potential difference and is given by

δv= e d

e= electric field

d= distance=5 mm=0.005 m

δv=2.4 (0.005)=0.012 v

now electric potential energy= u= q δv

u=6 (0.012)

u=0.072 j