Concept explainers
What can you say about the velocity of a moving body that in dynamic equilibrium? Draw a sketch of such a body using clearly labeled arrows to represent all external forces on the body.
The velocity of a moving body that is dynamic equilibrium and sketch a diagram of such a body.
Answer to Problem 1CQ
The velocity of a body in dynamic equilibrium is a constant, both in magnitude and direction.
Explanation of Solution
Introduction:
A body is said to be in equilibrium if the total force on the body is zero. On this basis, there are two kinds of equilibria- static equilibrium and dynamic equilibrium. According to Newton's first law, a body continues to be in the state of rest or in the state of uniform motion in a straight line, unless acted upon by an external unbalanced force. Further, Newton's second law implies that an unbalanced force produces an acceleration.
The sum of the forces acting on a body which is in dynamic equilibrium is zero. Therefore, the body experiences no acceleration. As a result, its velocity does not change. Thus, the body which is in dynamic equilibrium moves with a constant velocity.
Consider a block of weight W, acted upon by a force F. The block is placed on a horizontal surface. The surface exerts an upward force FNcalled the normal force on the block. A force of friction f acts between the surface and the block. The block moves towards the right with a velocity v.
The forces W and FNare equal and opposite. Thus, the sum of the forces along the vertical direction is zero. If the applied force F and the force of friction f have equal magnitudes but they are directed opposite to each other. Thus, the net force along the horizontal is also equal to zero. The sum of the forces acting on the block, being zero, the block is not accelerated. Thus, the velocity of the block remains constant. It continues to move with the same speed v and in the same direction.
A diagram representing the forces is shown below.
Conclusion:
A moving body under dynamic equilibrium moves with a constant velocity.
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