PHY130-SCCC Normal 17. An object having an initial momentum that he vector above

Question

PHY130-SCCC Normal 17. An object having an initial momentum that he vector above may be represented by t strikes an object that is initially at rest. Which of the following sets of vectors may represent the momenta of the two objects after the collision? 19. A 2 kg ball collides with the floor at an angle 0 and rebounds at the same angle and speed as shown above. Which of the following vectors represents the impulse exerted on the ball by the floor? 20. For a particular nonlinear spring, the relationship between the magnitude of the applied force F and the resultant displacement x from equilibrium is given by the equation -k x2. What is the amount of work done by stretching the spring a distance xo? 18. The escape speed for a rocket at Earth's surface is ve. What would be the rocket's escape speed from the surface of a planet with twice Earth's mass as Earth? and the same radius (a) 2 ve (e) 2

Explanation / Answer

17) (E)

Momentum is conserved. That means the vector sum of all the momentum vectors BEFORE the collision, must be equal to the vector sum of all the momentum vectors AFTER the collision.

The "Before" situation is represented by the top vector. So your job is to find a set of "After" vectors which, when summed, will equal the "Before" vectors.

(In other words, you want the "After" vectors to sum up to a vector about 1 inch long, pointing horizontally to the right).

So:

a) The vector sum of these two vectors is zero. (Two equal-length vectors pointing in opposite directions always sum to zero). That won't do.

b) The vector sum of these, is a 2-inch long vector pointing to the right. Too long.

c) The vector sum of these, is an (about) 1.5-inch long vector pointing to the right. Too long

d) Since these vectors are pointing in different directions, use the "parallelogram" method to sum them. From that you should be able to see that the resultant vector points diagonally down and to the right. Wrong direction.

e) Use the "parallelogram" method again. The resultant points horizontally to the right an is about 1 inch long. Correct.

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