h3. Part A
!pushbox2_1.png|width=400!
{excerpt}A person pushes a box of mass 15 kg along a smooth floor by applying a force _F_ at an angle of 30° below the horizontal.{excerpt} The box accelerates horizontally at a rate of 2.0 m/s{color:black}^2^{color}. What is the magnitude of _F_?
h4. Solution
{toggle-cloak:id=sysa} *System:* {cloak:id=sysa}Box as [point particle].{cloak}
{toggle-cloak:id=inta} *Interactions:* {cloak:id=inta}External influences from the person (applied force) the earth (gravity) and the floor (normal force).{cloak}
{toggle-cloak:id=moda} *Model:* {cloak:id=moda}[Point Particle Dynamics].{cloak}
{toggle-cloak:id=appa} *Approach:*
{cloak:id=appa}
{toggle-cloak:id=diaga} {color:red} *Diagrammatic Representation* {color}
{cloak:id=diaga}
Before writing [Newton's 2nd Law|Newton's Second Law] for the _x_ direction, we choose coordinates and break the applied force _F_ into x- and y-components:
!pushingboxmore1.png!
{cloak:diaga}
{toggle-cloak:id=matha} {color:red} *Mathematical Representation* {color}
{cloak:id=matha}
Using the free body diagram, we can write the relevant x-component of [Newton's 2nd Law|Newton's Second Law]:
{latex}\begin{large}\[ \sum F_{x} = F\cos\theta = ma_{x}\] \end{large}{latex}
Solving for _F_:
{latex}\begin{large}\[ F = \frac{ma_{x}}{\cos\theta} = \mbox{34.6 N}\]\end{large}{latex}
{cloak:matha}
{cloak:appa}
|