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Q. 51

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Found in: Page 130

### Physics for Scientists and Engineers: A Strategic Approach with Modern Physics

Book edition 4th
Author(s) Randall D. Knight
Pages 1240 pages
ISBN 9780133942651

# Problems 42 through 52 describe a situation. For each, draw a motion diagram, a force-identification diagram, and a free-body diagram.A spring-loaded gun shoots a plastic ball. The trigger has justbeen pulled and the ball is starting to move down the barrel. Thebarrel is horizontal.

A free body diagram, force-identification and motion diagram of a ball that started to move down a horizontal barrel as a spring-loaded gun shoots it are given here. These diagram represent the all the forces acted on the ball and the direction of speed and its acceleration.

See the step by step solution

## Step 1: Motion diagram

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

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

* The shape or size of the ball 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 along left to right as the spring pushes the ball with an external force.

* The acceleration vector is directed along the right side that is in the same direction of the ball moving down the barrel.

Thus, the motion-diagram of the ball moving down the barrel is given below:

## Step 2: Force-identification diagram

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

1. We have to consider the object 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 person who is jumping from a bridge.
3. The following forces are acting on the object:
• The long-range gravitational force is acted the on the ball directly downwards and a normal force that is equal to the gravitational force is exerted on the ball as the ball is at rest on the surface of horizontal barrel.
• The spring exert a force on the ball for which it starts moving along left to right.
• The frictional force between the surface of the barrel and the ball is in action.
• 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 ball) as a dot at the origin of the coordinate axes considering the particle model.
• A long range gravitational force is acting on the ball directly downward which defines the weight of the ball.
• An upward normal force is acted on the ball as it is at a rest on the surface of a horizontal barrel.
• A spring-loaded gun pushes the ball forward with a force . So, the spring-force is directed along the motion of the ball.
• A kinetic-friction works due to the surface of the ball and uneven barrel while the ball is moving through the horizontal barrel. The frictional force acts opposite to the motion of the ball.
• The free-body diagram of the ball is given below: