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Introduction To Physics (PHYS 111N) HW4: Forces

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what is the direction of the net force acting on the object at position a?

University

Old Dominion University

Course

Introduction to Physics (PHYS 111N)

HW4: Forces
Due: 11:59pm on Tuesday, February 27, 2018
You will receive no credit for items you complete after the assignment is due. Grading Policy
Understanding Newton’s Laws
Part A
An object cannot remain at rest unless which of the following holds?
Hint 1. How to approach the problem
This problem describes a situation of static equilibrium (i.e., a body that remains at rest). Hence, it is appropriate to apply Newton’s 1st law.
Hint 2. Newton’s 1st law: a body at rest
According to Newton’s 1st law, a body at rest remains at rest if the net force acting on it is zero.

Part B
If a block is moving to the left at a constant velocity, what can one conclude?
Hint 1. How to approach the problem
This problem describes a situation of dynamic equilibrium (i.e., a body that moves at a constant velocity). Hence, it is appropriate to apply
Newton’s 1st law.
Hint 2. Newton’s 1st law: a body in motion
According to Newton’s 1st law, a body initially in motion continues to move with constant velocity if the net force acting on it is zero.

Part C
A block of mass is acted upon by two forces: (directed to the left) and (directed to the right). What can you say about the block’s
motion?
Hint 1. How to approach the problem
This problem describes a situation of dynamic motion (i.e., a body that is acted on by a net force). Hence, it is appropriate to apply
Newton’s 2nd law, which allows you to relate the net force acting on a body to the acceleration of the body.
Hint 2. Newton’s 2nd law
Newton’s 2nd law states that a body accelerates if a net force acts on it. The net force is proportional to the acceleration of the body and
the constant of proportionality is equal to the mass of the body. In other words,
,
where is the net force acting on the body, and and are the mass and the acceleration of the body, respectively.
Hint 3. Relating acceleration to velocity
Acceleration is defined as the change in velocity per unit time. Keep in mind that both acceleration and velocity are vector quantities.

Part D
A massive block is being pulled along a horizontal frictionless surface by a constant horizontal force. The block must be __________.
Hint 1. How to approach the problem

Part E
Two forces, of magnitude and , are applied to an object. The relative direction of the forces is unknown. The net force acting on the
object __________.
Check all that apply.
Hint 1. How to approach the problem
By definition, the net force is the vector sum of all forces acting on the object. To find the magnitude of the net force you need to add the
components of the two forces acting. Try adding the two forces graphically (by connecting the head of one force to the tail of the other).
The directions of the two forces are arbitrary, but by trying different possibilities you should be able to determine the maximum and
minimum net forces that could act on the object.
Hint 2. Find the net force when the two forces act on the object in opposite directions
Find the magnitude of the net force if both the forces acting on the object are horizontal and the 10-N force is directed to the right, while the
4-N force is directed to the left.
Express your answer in newtons.
Hint 1. Vector addition
The magnitude of the vector sum of two parallel forces is the sum of the magnitudes of the forces.

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Introduction To Physics (PHYS 111N) HW4: Forces

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