Two objects X and Y move directly towards each other. The objects have the same mass. Object X has a velocity of 5.0 m/s to the right. Object Y has a velocity of 3.0 m/s to the left.

Object X and object Y collide and stick together.
What is their velocity after colliding?
A 1.0 m/s to the left
B 1.0 m/s to the right
C 4.0 m/s to the left
D 4.0 m/s to the right

You have two photos of a person walking. one shows the person at the corner of third and main streets, the other shows the person at the corner of tenth and main streets. there are lampposts at every corner in this town, and the first picture shows it to be 10: 32: 00 exactly. the second picture shows it to be 10: 49: 30. you know three facts: (1) all of the clocks are synchronized; (2) there are exactly 12 equal-sized blocks per kilometer in this town; and (3) the streets that cross main in this area are numbered consecutively, with no interruptions. what is the person’s average speed in kilometers per hour?