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Q. 52

Physics for Scientists and Engineers: A Strategic Approach with Modern Physics
Found in: Page 130

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Short Answer

Problems 42 through 52 describe a situation. For each, draw a motion diagram, a force-identification diagram, and a free-body diagram.

A person on a bridge throws a rock straight down toward the

water. The rock has just been released.

The motion diagram states the velocity of the rock just after it is released.

The free-body diagram represents the forces acting on the rock when it is released and it approaches the water.

See the step by step solution

Step by Step Solution

Step 1: Motion diagram

* Consider the particle model for the diagram of the motion.

* Represent the rock as a dot and assume the mass of the ball is concentrated into a single point considering the particle model.

* Here the shape or size of the stone does not affect the velocity of it according to the particle model.

* The frame between the dots are increasing as the speed of the ball is increasing while approaching the water under the influence of gravitational acceleration on it.

* The acceleration vector is directed along the motion of the ball when it is just released.

Thus, the motion-diagram of the stone approaching the water is given below:

Step 2: Force-identification diagram

To identify the forces acted on the rock, we have to follow the given steps:

  1. We have to consider the rock in which the force is acting upon.
  2. Now we have to draw the image of the object and encircle it. Here the object is the rock that has been just released straight down towards water.
  3. In the given situation, only the long-range gravitational force is acted on the rock as it is released from a height and it moves along downwards under free fall.

Therefore, the force-identification diagram should be as given below:

Step 3: Free-body diagram

The free body diagram is a pictorial representation of an object under some forces where the objects act as the particle and the forces acting on the object.

To draw a free-body diagram, we have to follow some steps as given below:

  • Draw a coordinate system.
  • Identify all the forces acting on the object and draw the vector of the forces.
  • Represent the object (here, the rock) as a dot at the origin of the coordinate axes considering the particle model.
  • A long range gravitational force is acting on the rock due to the free fall of the rock along the water. The rock has been just released by a person from the bridge. So, there is no other forces acting on the rock as shown below:

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