1A.)A railroad car of mass 21700 kg moving with a speed of 3.36 m/s collides
and couples with another rail car of mass 41700 kg, moving in the same
direction with a speed of 1.34 m/s. What is the speed of the two coupled
cars after the collision?

1B.)A 0.455-kg ball traveling at 7.36 m/s west collides head on with a 1.01-kg
ball moving in the opposite direction at a velocity of 12.4 m/s. The 0.455-
kg ball rebounds at 15.4 m/s after the collision. Find the velocity of the
second ball. (use west as the positive direction)

(a) 2.03 m/s

(b) 2.15 m/s

Explanation:

(a)

From the law of conservation of momentum, the sum of initial momentum equals the sum of final momentum

Momentum, p=mv where m is the mass and v is the velocity

where is the common velocity, and are velocities of the first railroad car  and the second railroad car respectively, and are masses of the first railroad car  and the second railroad car respectively

Substituting the given figures then

(b)

Momentum, p=mv where m is the mass and v is the velocity

where and are initial velocities of the ball moving towards west and the other ball moving in opposite direction respectively, and are masses of the first railroad car  and the second railroad car respectively

Taking west as positive then the opposite direction will be negative hence

Note that when the 0.455 rebounds, it moves towards East and since we took West as positive that is why we give 15.4 as a negative value.

towards East

volleyball players can not touch the net while the ball is in play

a and c

c is 100% but i am confused in a