Momentum is conserved if and only if sum of all forces which are exserted on system equals zero. In our situation there are only internal forces, so by Newton's third law their vector sum is 0.
So
.
Kinetic energy of system at first:
. After:
. The secret is that other energy is in work of deformation forces (they in turn heat a bullet and a block).
Answer is A)
To solve this exercise, it is necessary to apply the concepts of conservation of the moment especially in objects that experience an inelastic colposition.
They are expressed as,

Where,
= mass of the skier
= mass of the cat
= initial velocity of skier
= initial velocity of cat
= final velocity of both
Re-arrange to find V_f we have,



Once the final velocity is found it is possible to calculate the change in kinetic energy, so




Therefore the amount of kinetic energy converted in to internal energy is 819J
-- If acceleration and velocity are in the same direction,
then the object is speeding up.
-- If acceleration and velocity are in opposite directions,
then the object is slowing down.
-- If acceleration is perpendicular to velocity, then the object
is moving on a circular curve at constant speed.
Answer:
Insulation helps to prevent that transfer of heat.