Question

Instructions: Answer the following questions on separate paper OR within the Word document or Libre office by adding space in between the questions. 1. If the acceleration of a system is zero, are no external forces acting on it? What about internal forces? Explain your answers. 2. If a constant, nonzero force is applied to an object, what can you say about the velocity and acceleration of the object? 3. When you take off in a jet aircraft, there is a sensation of being pushed back into the seat. Explain why you move backward in the seat-is there really a force backward on you? 4. Newton's third law of motion tells us that forces always occur in pairs of equal and opposite magnitude. Explain how the choice of the "system of interest" affects whether one such pair of forces cancels. 5. Identify all possible normal forces in the following diagram. There is a wall on the left side and of course a floor on the bottom. Here is an example of how to list them. (1) Normal force between the floor and block A J F G 1 H E D B C 6. Using the above figure for reference, draw the free body diagram for object L. 7. Using the above figure for reference, draw the free body diagram for object C.

Answer 1

1) if the acceleration of the system is zero , it means that no net external forces acts on the system . there is a possibility that a number of forces are acting on the system but the net effect of all these external forces will be zero.

internal forces are always present in the system but they always act in pairs and hence net effect of internal forces is always zero.

2) if a constant non zero force is applied to an object , then the velocity of an object changes uniformly with time that is , it keeps on increasing or decreasing at a uniform rate depending on the fact that the force is supporting the motion or retarding the motion respectively.

the acceleration in such a case is always constant , because acceleration = force/mass

and both force and mass are constant , so acceleration is also constant.

3) we feel a backward force because of the concept of inertia of rest. our body is initially at rest and it tends to remain in the state of rest due to the inertia of rest. but when the jet suddenly takes off , our lower body in contact with the jet moves ahead whereas the body applies a resistive force ( inertia) to remain at rest and hence we feel a backward force.

yes , a pseudo force acts on our body.