Determine whether the sign of heat or work (relative to the system) is positive or negative. a metal cylinder is rolled up a ramp. (the metal cylinder is the system.) the fireman extinguishes the fire with foam and cools the environment. (the foam is the system.)

Metal cylinder: Work is positive

Foam: Heat is positive.

Explanation:

Work is done as a resultant force acts along a displacement. Heat is the flow of energy from one body to another, resulting in a either a rise or a drop in temperature of the bodies. Work and Heat are forms of energy and they can either be assigned a positive or negative sign with respect to a thermodynamic system.

If work is done on a body (thermodynamic system), the work is negative. On the other hand, if work is done by the body, it is termed as a positive work. Heat is positive when it flows into a thermodynamic system and negative when it is lost by the system.

In this case, though the metal cylinder is rolled up a ramp, the metal cylinder does a positive work along the displacement. Considering the foam, heat is gained by the foam (thermodynamic system) as it cools the environment, thus, heat is positive.

(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