Chapter 4
1. (p.104 prob.7) What average force is required to stop an 1100-kg car in 8.0s if it is traveling at 90km/h?
2. (p. 105 prob.13) A 10-kg bucket is lowered by a rope in which there is 63N of tension. what is the acceleration of the bucket? Is it up or down?
3. (p.105 prob.19) A Saturn V rocket has a mass of 2.75 x 106kg and exerts a force of 33 x10N on the gases it expels. determine (a) the initial vertical acceleration of the rocket, (b) its velocity after 8.0s, and (c) ho long it takes to reach an altitude of 9500m. Ignore mass of gas expelled and assume g remains constant.
4. (p.106 prob.28) A person pushes a 14.5-kg lawn mower at constant speed with a force of 88.0N directed along the handler, which is at an angle of 45.0 to the horizontal (Fig.4-40). (a) Draw the free-body diagram showing all forces acting on the mower. Calculate (b) the horizontal retarding force on the mower, then the normal force exerted vertically upward on the mower by the ground, and (d) the force the person must exert on the lawn mower to accelerate it from rest to 1.5m/s in 2.5seconds (assuming the same retarding force).
5. (p.108 prob.45) two crates, of mass 75kg and 110kg, are contact and at rest on a horizontal surface (Fig.4-47). A 730-N force is exerted on the 75kg crate. If the coefficient of kinetic friction is 0.15, calculate (a) the acceleration of the system, and (b) the force that each crate exerts on the other.
6. (p.109 prob.55) A roller coaster reaches the top of the steepest hill with a speed of 6.0km/h. It then descends the hill, which is at an average angle of 45° and 45.0m long. what will its speed be when it reaches the bottom? Assume mk = 0.12.