Answer:
The mass is 
Explanation:
From the question we are told that
The initial temperature is 
The final temperature is 
Generally the maximum heat produced by 1 Liter of natural gas is 
So the amount of heat produced by 100 L is
=> 
Generally given that the efficiency is 
Then actual heat received by the water is
=> 
=> 
Converting to kcal
=> 
Generally the specific heat of water is
Generally the heat received by the water is mathematically represented as
=> 
=>
Answer:
Newton's First Law of Motion
Explanation:
Without external forces acting on an object, the object tends to move at constant speed in a straight line. This property is referred to as inertia. Newton's first law states this natural observation.
The key to solve this problem is the conservation of momentum. The momentum of an object is defined as the product between the mass and the velocity, and it's usually labelled with the letter 
:
The total momentum is the sum of the momentums. The initial situation is the following:
(it's not written explicitly, but I assume that the 5-kg object is still at the beginning).
So, at the beginning, the total momentum is
At the end, we have
(the mass obviously don't change, the new velocity of the 15-kg object is 1, and the velocity of the 5-kg object is unkown)
After the impact, the total momentum is
Since the momentum is preserved, the initial and final momentum must be the same. Set an equation between the initial and final momentum and solve it for 
, and you'll have the final velocity of the 5-kg object.
The correct answer is 1.2 m/s
: mv+mv=mv+mv
(0.5kg)(2m/s)+(0.4kg)(0m/s)=(0.5kg)v+(0.4kg)(1m/s)
= 1kg*m/s=(0.5kg)v+0.4kg*m/s
=1kg*m/s-0.4kg*m/s=(0.5kg)v
=0.6kg*m/s=(0.5kg)v
to solve for v we divide both side by 0.5kg
v=1.2m/s
