Newton's Laws & Universal Law of Gravitation Sample Problems

1. What gravitational force exists between two 3 kg balls placed 7.25 m apart?
2. A sphere weighing 9800 N and another sphere weighing 1960 N are separated by 4 m. What gravitational force exists between them?
3. A 20 N force gives a stone an acceleration of 4 m/s2. What is the weight of the stone?
4. A 5 kg rocket is acted upon by an upward force of 59 N due to the thrust produced by its engines. What is the rocket's weight? Draw the free-body diagram representing these forces. What is the unbalanced force? What acceleration does it cause?
5. A rope attached to an 80 N wagon pulls it horizontally to the right with an acceleration of 0.5 m/s2. What is the mass of the wagon? What is the unbalanced force causing this acceleration?
6. A 65 N boy sits on a sled weighing 52 N on a horizontal surface. The coefficient of friction between the sled and the snow is 0.012. What is the magnitude of the frictional force? The sled is pulled at constant speed by a rope held horizontally. What is the tension (the pull) in the rope?
7. A 100 N force is applied to a 10 kg box to push it across a horizontal surface. A frictional force of 20 N exists. What is the acceleration of the box?
8. An object weighing 40 N rests on a surface. The coefficient of friction between the surface and the object is 0.35. What is the frictional force between the object and the surface? A 20 N force is applied to pull the object horizontally. What is the magnitude of the unbalanced force? What is the acceleration of the box?
9. A rocket of mass "m" is accelerated upward by a force giving it an acceleration of 3 g (or three times the acceleration due to gravity). What is the magnitude of this force in terms of "m" and "g?"