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)
Answer:
Question 1)
a) The speed of the drums is increased from 2 ft/s to 4 ft/s in 4 s. From the below kinematic equations the acceleration of the drums can be determined.
This is the linear acceleration of the drums. Since the tape does not slip on the drums, by the rule of rolling without slipping,
where α is the angular acceleration.
In order to continue this question, the radius of the drums should be given.
Let us denote the radius of the drums as R, the angular acceleration of drum B is
α = 0.5/R.
b) The distance travelled by the drums can be found by the following kinematics formula:
One revolution is equal to the circumference of the drum. So, total number of revolutions is
Question 2)
a) In a rocket propulsion question, the acceleration of the rocket can be found by the following formula:
b)