Newton's Laws - Mission NL8 Detailed Help

Analyze the free body diagram shown at the right and determine which of the following statements are true of the object.


 
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The relationship between net force (Fnet), mass (m) and acceleration (a) is expressed by the equation
 
Fnet = m•a


 
Speeding Up, Slowing Down, and the Direction of Acceleration:
If an object is moving to the right and accelerating to the left, then the object must be slowing down. If an object is moving to the right and accelerating to the right, then the object must be speeding up.

Slowing down motions are characterized by an acceleration value which is opposite the direction of motion.


 
There are several statements to evaluate in this question. A careful and thoughtful application of physics principles will be required to be successful.
 
Consider the statements about the mass and the weight of the object: The weight is the force of gravity which acts upon an object and the mass of an object on Earth is approximately 1/10-th its weight (from the formula Fgrav= m•g).
 
Consider the statements about the acceleration magnitude and direction. The direction of the acceleration is in the same direction as the unbalanced force. If there is more force to the left than to the right, then the object is accelerating to the left. And the magnitude (or numerical value) of the acceleration is the ratio of net force to mass. So find the mass from the object's weight and find the net force from the vector sum of all individual forces.
 
Finally, consider the statements about the direction that the object moves and whether it is speeding up or slowing down. If friction is considered a resistance force, then this object is moving opposite the direction of the friction force. Knowing the direction that it is moving and the direction of the acceleration will allow you to make a conclusion about whether the object is speeding up or slowing down. (See the Know the Law section.)


 

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