Physics Challenge Question 8 Solutions Part 1 T FN

physics challenge question 8: solutions part 1 t fn = mg he trailer is not moving, so the forces acting on it must sum to 0, by

Physics Challenge Question 8: Solutions
Part 1
T
FN = mg
he trailer is not moving, so the forces acting on it must sum to 0, by
Newton’s first law. The only forces acting on it are gravity and the
ground’s normal force.



Fg = mg
Part 2
The free-body diagram is the same as before with two new forces added
to it. The net force is no longer 0.
Ff
Fpull

Fg = mg
FN = mg

Part 3
Looking at our free-body diagram from the previous part, we see that
the vertical forces cancel. (The trailer is not accelerating into the
ground or off the Earth!) So let’s write down Newton’s second law for
the horizontal direction:


Since the rope broke, the trailer must have had a mass of at least
2,000 kg. (We used 7,000 N in our calculations, because that was the
smallest force that could break the rope. We don’t know for sure that
it wasn’t in fact larger!)
Part 4
The vertical forces (gravity and the normal force) still cancel. Note
that the 2,000 N is the net force, i.e. the force of the pulling minus
friction. As the wind pushes it sideways, we can draw the following
free-body diagram, now viewed from above:
Fnet = 2,500 N
Fwind = ?

Fpull = 2,000 N


Since these two forces are pointing in different directions (one is
left/right, and the other is forward/backward), we have to be careful
when adding them. Since they form a right-angled triangle, let’s use
the Pythagorean theorem: