Question

A body of mass 1.50kg is dropped from a height of 12m. What is the force acting on it during its fall? (g=9.8m/sec)

Answer 1

Some of the conventions in these notes are different from conventions in some textbooks. Although
some of these are controversial and may incur the ire of other physics teachers, here is an explanation
of my reasoning:
 When working sample problems, the units are left out of the algebra until the end. While I agree
that there are good reasons for keeping the units to show the dimensional analysis, many
students confuse units for variables, e.g., confusing the unit “m” (meters) with the variable “m”
(mass).
 Problems are worked using
2
m
s
g 10
. This is because many students are not adept with algebra,
and have trouble seeing where a problem is going once they take out their calculators. With
simpler numbers, students have an easier time following the physics.
 Vector quantities are denoted with arrows as well as boldface, e.g.,
, , g
v d F
. This is to help
students keep track of which quantities are vectors and which are scalars.
 Forces are denoted the variable
F
with a subscript, e.g.,
, , ,
g f N T F F F F , etc. instead of
mg f N T , , , ,
etc. This is to reinforce the connection between a quantity, a single variable, and a unit.
 Average velocity is denoted
ave.
v
instead of
v
. I have found that using the subscript “ave.” makes
students less likely to forget that average velocity is different from initial and final velocity.
 The variable V is used for electric potential, and ΔV for potential difference (voltage). Although
  V RI
is different from how the equation looks in most physics texts, it is useful to teach
circuits starting with electric potential, and to maintain the distinction between absolute electric
potential and potential difference. (This is also how the College Board represents voltage on the
AP® Physics exams.)
 Equations are typeset on one line when practical. While there are very good reasons for teaching
net
m

F
a
rather than
F a net
m
and
V
R

I 
rather than
  V RI
, students’ difficulty in solving for
a variable in the denominator often causes more problems than does their lack of understanding
of which are the independent and dependent variables.

Answer 2

f = MGH
f = 1.50 * 0.012 * 0.098
f = 0.001764