Which statement about the physical change of liquid water boiling into steam is true?

a. the heat added represents an energy change.
b. the action cannot be reversed.
c. the steam cannot conserve mass.
d. the weight lost represents a mass change

Answer is: a. The heat added represents an energy change.

The same substance is present before and after the psysical change (chemical composition is not changed), just with different form (shape) or state of matter.

Liquid water molecule gain heat (energy) and move faster (higher kinetic energy).

The average kinetic energy of molecules depends on the temperature, steam has higher temperature.

(newtons first law)

conservation of momentum law states :

momentum before collision = momentum after collision

momentum p (kg-m/s)= mass * velocity

say moving car=1 000 kg, velocity = 10 m/s then p = 1 000*10= 10 000 kg-m/s

say still car = 2 000 kg, velocity = 0 m/s then p = 2 000* 0 = 0 kg-m/s

total momentum prior to collision = 10 000 + 0 = 10 000 kg-m/s

momentum after collision = 10 000 kg-m/s

mass now = 1 000 kg+2 000 kg = 3 000 kg

10 000 = 3 000 kg* velocity m/s

10 000/3 000 = velocity

3.33 m/s = velocity after collision

an impulse is a force applied over time , momentum is exclusive of external forces and a perfect collision is implied