# Expert Answers

1. Two balls of equal mass move at the same speed in different directions. Are their momenta equal? Explain.

2. A sport utility vehicle is travelling at a speed of 15.7 m/s. If its momentum has a magnitude of 32,800 kg•m/s, what is the SUV’s mass?

3. A net force of 30 N is applied to a 10 kg object, which starts at rest. What is the magnitude of its momentum after 3.0 seconds?

4. Nitrogen gas molecules, which have mass 4.65×10−26 kg, are striking a vertical container wall at a horizontal velocity of positive 440 m/s. 5.00×1021 molecules strike
the wall each second. Assume the collisions are perfectly elastic, so each particle rebounds off the wall in the opposite direction but at the same speed. (a) What is the change in momentum of each particle? (b) What is the average force of the particles on the wall?

5. How far is the center of mass of the Earth-Moon system from the center of the Earth?
The Earth’s mass is 5.97×1024 kg, the Moon’s mass is 7.4×1022 kg, and the distance between their centers is 3.8×108 m.

6. The uniform sheet of siding shown has a centrally-located doorway of width 2.0 m and height 6.0 m cut out of it. The sheet, with the doorway hole, has a mass of 264 kg. (a)
What is the x coordinate of the center of mass? (b) What is the y coordinate of the center of mass? Assume the lower left hand corner of the siding is at (0, 0).