16. If there is no external force acting on the system,

which BEST describes the momentum of two objects

before and after a collision?

The momentum before collision is __________

the momentum after collision.

A. double than

C. greater than

B. equal to

D. less than

17. Two billiard balls approach each other at equal speed.

If they collide in a perfectly elastic collision, what

would be their velocities after collision?

A. zero

B. same in magnitude and direction

C. same in magnitude but opposite in direction

D. different in magnitude and opposite in direction

18. Which principle explains why airbags are installed in

automobiles?

A. The momentum of an isolated system is conserved

B. Decreasing the time of contact increases impact force.

C. Increasing the time of contact decreases impact

D. The airbags increase the momentum of the system.

force.

19. A sepak takraw ball is hit vertically upward by a

player. What is the acceleration after 1 second?

A. 0 m/s2

C. 9.8 m/s2

B. 1 m/s2

D. -9.8 m/s2

20. Why do we need to fasten our seatbelt when riding a

vehicle?

A. To increase momentum during sudden stop

B. To have zero velocity during sudden stop

C. To have constant velocity during sudden

stop

D. To decrease momentum during sudden

stop​