Q4.94: a man runs as fast as he can along a moving sidewalk from one end to the other, taking 3.0 s. he then runs as fast as he can back along the moving sidewalk to his starting point, taking 15 s. what is the ratio of the sidewalk’s speed to the man’s running speed?

Explanation:

Given

Man takes 3 s while running along the sidewalk

and 15 s while running opposite to sidewalk

Let the speed of man and sidewalk be v and v_0 and distance between the two endpoints of sidewalk is x

Now ----------1

Also ----------2

Divide 1 & 2

the answer is the first electromagnet (a). this is because it has more coils around the ferromagnetic material. increasing the number of coils increases the surface area in which the metal interacts with the current in the coil. this enables more atoms in the metal to become aligned hence becoming more magnetized.