Part A
A 10 kg box slides at a constant speed of 2 m/s along a smooth floor. What is the magnitude of the normal force exerted on the box by the floor?
System: Box as point particle subject to external influences from the earth (gravity) and the floor (normal force).
Model: Point Particle Dynamics.
Approach: We begin with a free body diagram for the box:
From the free body diagram, we can write the equations of Newton's 2nd Law. We ignore the x-direction, since there are no forces acting.
Unknown macro: {latex}
\begin
Unknown macro: {large}
[ \sum F_
Unknown macro: {y}
= N - mg = ma_
]\end
Because the box is sliding over level ground, it is not moving at all in the y direction. Thus, it certainly has no y-acceleration. Setting ay = 0 in the above equation gives:
Unknown macro: {latex}
\begin
Unknown macro: {large}
[ N = mg = 98 N]\end