**Unit 8: Newton's Laws of
Motion**

**Problem Set A**

**Overview:**

Problem Set A targets your understanding of Newton's second law of motion and of the distinction between mass and weight. There are a few routine problems and several more complicated multistep problems. The mathematical rigor of the problem set is not high; most student difficulties will lie in the area of conceptual misunderstandings. There are at least four skills needed to be successful on Problem Set A:

- A strong conceptual understanding of the relationship and
distinction between mass and weight. Mass is a quantity which is
dependent upon the amount of matter present within an object; it
is measured in kilograms and is independent of location. Weight,
on the other hand, is the force of gravity which acts upon an
object. Since gravitational forces vary with location, the weight
of an object on the Earth's surface is different than its weight
on the moon. Being a force, weight is expressed in the metric unit
as Newtons. Every location in the universe is characterized by a
gravitational constant represented by the symbol
**g**(sometimes referred to as the acceleration of gravity). Weight (or F_{grav}) and mass are related by the equation: F_{grav}= m • g. - An ability to manipulate the F
_{net}= m•a equation in order to solve for an unknown quantity. Additionally, a student will need to understand the meaning of net force as the vector sum of all individual forces acting upon an object. If all individual forces are known, the net force can be calculated by simply*adding*the individual forces while paying attention to their vector nature. An up force and a down force can be*added*by assigning the down force a negative value. A right force and a left force can be*added*by assigning the left force a negative value. - An ability to use the F
_{net}= m•a equation as a guide to thinking about how alterations in the mass of or net force acting upon an object will subsequently effect the acceleration of the object. Rather than using the equation as an algebraic recipe for problem-solving, one will have to use it to think about how a twofold, threefold or X-fold increase or decrease in one of the variables would effect the acceleration value. - An ability to use a kinematic equation to solve for an unknown
kinematic quantity. Kinematics pertains to a description of the
motion of an object and focuses on questions of
*how far?*,*how fast?*,*how much time?*and*with what acceleration?*To assist in answering such questions four kinematic equations were presented in the 1-Dimensional Kinematics unit:-
**d = v**_{o }• t + 0.5 • a • t^{2}**v**_{f }= v_{o }+ a • t**v**_{f}^{2}= v_{o}^{2}+ 2 • a • d**d = [( v**_{o}+ v_{f }) / 2 ] • t

Newton's laws and kinematics share one of these questions in common:

*with what acceleration?*The acceleration of the F_{net}= m•a equation is the same acceleration of the kinematic equations. Common tasks thus involve i) using kinematics information to determine an acceleration and then using the acceleration in a Newton's laws analysis, or ii) using force and mass information to determine an acceleration value and then using the acceleration in a kinematic analysis. -

**Additional Readings/Study
Aids:**

The following pages from The Physics Classroom tutorial may serve to be useful in assisting you in accomplishing the above tasks.

View Sample Problem Set.

Return to: Set A Overview Page || Audio Help Home Page || Set A Sample Problems

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