a block mass m1 collides with a block of mass m2 such that m1 becomes at rest and m2 slides across the surface until it reaches the frictional surface. the coefficient of friction between m2 and surface is uk. What is the rate of change of the speed of the center of mass of the two block system after m2 enters frictional surface

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.

there are no contact forces mentioned on the list of choices that you've provided.

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.