Answer:
B. Hold each type of fabric over a candle flame and time how long it takes for the fabric to start to burn.
Explanation:
Given
Car 1
m1 = 1300 kg
v1 = 20 m/s
m2 = 900 kg
v2 = -15 m/s
(Negative sign shows that direction of car 2 is opposite to car 1)
Procedure
As per the conservation of linear momentum, "The total momentum of the system before the collision must be equal to the total momentum after the collision". And this applies to the perfectly inelastic collision as well. Then the expression is,

Thus, we can conclude that the speed and direction of the cars after the impact is 5.68 m/s towards the first car.
Explanation:
Equation for energy balance will be as follows.


Hence, 
Therefore, we will calculate the final temperature as follows.

= 868.03 R
Now, we will calculate the mass as follows.
m = 
= 
= 1.031 lbm
Hence,

Putting the values into the above equation as follows.


= 655.2 Btu
Thus, we can conclude that work done by paddle wheel is 655.2 Btu.