1.

2. a, b, and d. Friction and the normal force are the only contact forces. Nothing is touching the rock to provide a “force of the kick.”

3. b. Acceleration is proportional to force, so doubling the number of rubber bands doubles the acceleration of the original object from $2\text{m}\text{/}{\text{s}}^{2}to4\text{m}\text{/}{\text{s}}^2$. But acceleration is also inversely proportional to mass. Doubling the mass cuts the acceleration in half, back to $2\text{m}\text{/}{\text{s}}^2$.

4.

5. c. The acceleration vector points downward as the elevator slows. $\overrightarrow{F_{}}{}_{\text{net}}$ points in the same direction as $\vec{a}$, so $\overrightarrow{F_{}}{}_{\text{net}}$ also points down. This will be true if the tension is less than the gravitational force: $T<F_G$.

1. Gravity, tension

3. Gravity, normal force, kinetic friction

5. Gravity, normal force, thrust, drag

7. 3

9. 18 N

11. $-2\times {10}^{33}\text{J}$

13.

1. 1

2. 2

15. 1.8 N

17.

19.

21.

23.

25.

27.

29.

31.

33.

1. $16\text{m}\text{/}{\text{s}}^2$

2. $4.0\text{m}\text{/}{\text{s}}^2$

3. $8.0\text{m}\text{/}{\text{s}}^2$

4. $32\text{m}\text{/}{\text{s}}^2$

35.

37.

39.

41.

• a.

  

  Full Alternative Text

• b. Yes. $0{\text{m/s}}^2\text{,}0\text{N}$

• c. 57 kg

43.

45.

47.

49.

51.

53.

55.

57.