Chapter 4 Newton's Second Law of Motion
Exercises
9. Shake or push the Box and the one with the most resistance is the box with sand.
11. The cleaver has more mass and inertia to cut through vegetables.
13. Mass and weight do not change when it is crushed.
17. 1 kg = 2.2 lb = 9.8 N. Your weight can be expressed in Newtons and your mass can be expressed in kg.
23. Mass does not affect the acceleration due to gravity (g), but it does affect the Force when it hits.
 | If Weight = mass * g ; then |
| g = W/mass. |
| g does not change! |
28.
| (a) No, air resistance is present to slow the speed. |
| (b) Yes, no air resistance above the atmosphere. The satellite velocity is enough to keep the rate of fall per second less than the distance to hit the earth. |
32. Greater. If W = Fg = m * g , you would push with more force than your weight to leave the ground.
56. If the balls were the same size, the heavier ball may hit the ground first. But not in ½ the time of the lighter ball.
Problems
4. F = ma, so
| a = F/m |
| a = 2 N/2 kg |
| a = 1 m/s2. |
It is the same acceleration.
5. Four engines produce 120,000 N of force, so
| a = F/m |
| a = 120,000 N / 30,000 kg |
| a = 4 m/s2. |
7. Fnet = m * a, so
| Fnet = 80 kg * -4 m/s2 |
| Fnet = -320 N. |
8.
| ½ W up + Fg down = m * a, |
| ½ mg up + mg down = m * a, |
| a = ½ g down. |
9.
| (a) a = 1 m/s / 2 s = 0.5 m/s2. |
| (b) Fnet = m * a = 60 kg * 0.5 m/s2 = 30 N. |