TUTORIAL SESSION 4 – Force and Motion
1. State Newton’s first law of motion.
2. When you are standing in a bus if the bus starts to move forward you tend to jolt backwards. When the bus comes to a stop you tend to jolt forward. Explain this in terms of Newton’s first law.
3. What do we mean by reference frame? What is an inertial reference frame?
4. State Newton’s second law of motion.
5. If two forces act on a body can the body move with a constant velocity? Can it remain at rest? Give examples to support your answers.
6. What is the difference between the weight of an object and its mass?
7. A student pulls a sled of mass 60kg across a frictionless surface with a force of 100 N directed at 30° to the horizontal. Draw a free-body diagram showing all the forces acting on the sled and calculate the horizontal acceleration.
8. Two masses are connected by a rope and pulled along by a constant force of 50 N. Draw a free-body diagram for each mass and calculate the acceleration of the masses and the tension in the rope.
9. Calculate the tensions in each of the segments of rope in the following diagram. The masses are at rest. Draw a free-body diagram for each mass.
10. A mass is suspended from a ceiling by two cords. If the mass is 5.0 kg find the tension in each cord. Draw a free-body diagram indicating all the forces on the mass.
11. A mass, 2.0 kg, is sliding down a frictionless inclined plane of angle 30°. What is the acceleration of the mass? Draw a free-body diagram indicating all the forces acting on the mass. (Hint choose the co-ordinate axes to be parallel and perpendicular to the surface).
12. Two masses are connected by a pulley as shown in the diagram below. Draw free-body diagrams for the masses and find the tension in the rope and the acceleration of the masses.
13. A man is standing in an elevator. Draw a free-body indicating the forces acting on the man and calculate the normal force acting for the following situations
a) elevator is stationary
b) elevator is accelerating upwards at 2.0 m.s-2
c) elevator is accelerating downwards at 1.5 ms-2.
14. A 10 kg monkey climbs up a massless rope that runs over a frictionless tree limb and back down to a 15 kg package on the ground.
a) What is the magnitude of the least acceleration the monkey must have if it is to lift the package off the ground?
b) If after the package is lifted the monkey stops climbing and holds onto the rope what is its acceleration?
15. State Newton’s third law.
16. Consider the two masses shown below. A force of 10 N acts on mass m1 (3.0 kg). It applies a force on m2 (2.0 kg). According to Newton’s third law m2 must apply and equal and opposite force on m1. Show that these forces are equal and opposite (calculate them). What is the acceleration of the two masses? Why don’t these forces cancel to produce no acceleration?
17. A boy walks along pulling a cart on a rope. Draw all the ‘action-reaction’ pairs. (Hint you must consider friction if he is walking)
Student Learning
Summarise the three most important aspects from this topic.
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