When a driver brakes an automobile, the friction between the brake drums and the brake shoes converts the car's kinetic energy to thermal energy. if a 1500-kg automobile traveling at 35 m/s comes to a halt, how much does the temperature rise in each of the four 8.0 kg iron brake drums? (the specific heat of iron is 448 j/(kg · °

64.1°C

Explanation:

mass of automobile, M = 1500 kg

velocity, v = 35 m/s

mass of each brake, m = 8 kg

specific heat of iron, c = 448 J/kg°C

According to the conservation of energy

the kinetic energy of automobile = thermal energy of brakes

0.5 Mv² = 4 x m x c x ΔT

where, ΔT is the rise in temperature of the brake

0.5 x 1500 x 35 x 35 = 4 x 8 x 448 x ΔT

ΔT = 64.1°C

Thus, the change in temperature of each brake is 64.1°C.

area of focus

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.