Answers to even questions in Chapter 4.   Notify me of any disagreement.

2. Average force is 25 N.
4. Time taken is 7.4 min.
6. Average force is 312 N.
8. a) Total force has magnitude 799 N at angle 8.8 deg. to right of center. 
   b) Magnitude of acceleration is 0.266 m/s^2.
10. Average force is 1.1*10^4 N.
12. Tension is 77.8 N.
14. Weight should be 171 N and angle should be 61 deg.
16. Resistive force is 1040 N.
18. a) Distance moved without child is 1.5 m.
    b) Distance moved with child is 1.4 m.
20. Acceleration is 4.43 m/s^2.  Tension is 53.7 N.
22. a) New speed is 51.3 km/hr.
    b) Distance travelled is 589 m.
24. Speed at 80 m up hill is 7.90 m/s.
26. Tension in upper rope is 236 N.  Tension in lower rope is 118 N.
28. a) Tension in rope is 36.8 N.
    b) Acceleration is 2.45 m/s^2.
    c) Distance moved in 1st second is 1.23 m.
30. a) System will not move since tension is less than limiting friction.
    b) Once moving, acceleration is 0.70 m/s^2.
32. a) Average acceleration is -1.20 m/s^2.
    b) Average coefficient of kinetic friction is 0.122.
34. Time to move 4.00 m is 3.17 sec.
36. a) Acceleration of box is 0.366 m/s^2.
    b) Box will not move since frictional force is less than limiting value!
38. a) Minimum stopping distance on wet surface is 98.4 m.
    b) Minimum stopping distance on dry surface is 16.4 m.
40. a) Acceleration of masses is 0.125 m/s^2.
    b) Tension in the string is 39.7 N.
    c) Coefficient of kinetic friction is 0.234.
42. a) Minimum F is 18.5 N.
    b) Normal force is 25.8 N.
44. a) Time taken to cross 8.00 kg block is 2.13 sec.
    b) Distance moved by 8.00 kg block is 1.66 m.
46. Average force on ball is 20.0 N.
48. a) Minimum frictional force for equilibrium is 490 N.
    b) Coefficient of static friction required is 0.500.
    c) Hanging mass for constant speed is 25.0 kg.
50. Coefficient of kinet friction is 0.814.
52. a) Acceleration of system is 1.63 m/s^2.
    b) Tension in long string is 57.2 N.  Tension in short string is 24.5 N.
54. a) See solution for force diagram.
    b) Tension in cord is 9.8 N.
    c) Acceleration of sled is 0.58 m/s^2.
56. a) See solution for force diagram.
    b) Acceleration of system is 5.8 m/s^2.
    c) Tension in first rope is 17 N.  Tension in second rope is 41 N.
58. Acceleration of rail car is 0.69 m/s^2.
60. Maximum force is 56.0 N.
62. Retarding force required from parachute is 550 N.
64. a) Angle of incline is 30.7 deg.
    b) Tension in string is 0.843 N.
66. a) Before starting spring scale registers weight, ie mg, which is 706 N.
    b) During acceleration spring scale registers m(g+a), which is 814 N.
    c) At constant speed spring scale registers weight again, ie 706 N.
    d) During deceleration  spring scale registers m(g+a), which is 648 N.
68. a) See solution for details.
    b) T_1 is 514 n.  T_2 is 558 N.  T_3 is 325 N.
70. Force of air resistance is 5100 N.