 ### Newton’s Laws & Universal Law of Gravitation

1. Determine the acceleration that a 25 N unbalanced force gives to a 4 kg mass. Ans: 6.25 m/s2
2. A racing car weighs 6958 N. What is its mass? If it starts from rest and travels 12 m in 2 sec, what is its acceleration? What unbalanced force caused this acceleration? Ans: 710 kg; 6 m/s2, 4260 N
3. An 8 kg ball is separated from a 6 kg ball by 2 m. What is the gravitational force of attraction between them? Ans: 8 x 10-10 N
4. Two satellites of equal mass are put into 30 m apart. A gravitational force of 2 x 10-7 N acts between them. What is the mass of each satellite? What is the initial acceleration given each satellite by this force? Ans: 1643 kg; 1.22 x 10-10 m/s2
5. A rubber ball weighs 49 N. It is thrown upward with a force of 69 N. What is the unbalanced force? What acceleration does it cause? Ans: 20 N; 4 m/s2
6. An object with a mass of 22.7 kg is placed on a horizontal surface. The mass moves horizontally at constant speed. The coefficient of friction between the two surfaces is 0.94. What is the force of friction? Ans: 209.11N
7. It takes 50 N to pull a 6 kg object along a desk at constant speed. What is the coefficient of friction? Ans: 0.85
8. A boy pushes horizontally on a 10 kg wagon and it accelerates at 2.5 m/s2. If frictional forces total 50 N, what force is he exerting on it? Ans: 75 N
9. The mass of an elevator plus occupants is 752 kg. The tension in the cable supporting the elevator is 8950 N. What is the unbalanced force? What is the elevator’s acceleration? Ans: 1580.4 N; 2.10 m/s2
10. A pulley holds a 10 N weight. A man pulls on the rope with an upward force of 15 N. What acceleration does the weight experience? Ans: 4.90 m/s2
11. A 800 N force pushes a 50 kg block horizontally on a table. The coefficient of friction between the surfaces is 0.60. What force of friction opposes the motion? What is the unbalanced force? What is the block’s acceleration? Ans: 294 N; 506 N; 10.12 m/s2
12. A bicycle with a mass of 3.1 kg feels a frictional force of 21 N retarding its motion. A 50 N force is applied by the bicyclist on the wheel. What is the coefficient of friction between the bicycle and the road. What acceleration does it experience? Ans: 0.69; 9.35 m/s2