Phy 121 - Assignment 2
A. 1. Doesn’t matter. The initial velocity is horizontal, so it has no effect on how
long it takes the bullet to fall vertically to the ground.
2.
B. 1. (This question illustrates the difference between addinig vectors and adding
scalars.)
a. Zero: Displacements are vectors, so you add them like this:
When you draw the resultant from where you started to where you
end up, it has a length of 0 (and no particular direction) because
where you started is where you end up.
b. 560 m: Distance is a scalar, so you add them like this: 140 + 140 + 140 + 140 =
560
2. Step 1: Pick a scale: Have it as large as you can without going off the edge of the
paper, because the larger the diagram is, the more accurate. I did 1 inch = 1 m on my
original, although it might not quite print out that size.
Step 2: Draw A, then draw B coming off A’s arrowhead. Measure their lengths with a
ruler and their directions with a protractor.
C. 1. No, never. The magnitude of a vector is just how “long” it is, regardless of
its direction. (Similar to the absolute value of a scalar, hence the use of the same
symbol.)
2.
D. a.
So, vx = 13.1 m/s , vy = 20.1 m/s , ax = 0 , vy = –9.8 m/s2
b. A projectile’s horizontal velocity is constant. So if it started at 13.1 m/s, it will
still be 13.1 m/s. Its vertical velocity behaves just like a ball thrown straight up;
this would be zero at the maximum height. A freely falling object’s acceleration is
always the same thing regardless of its velocity, so ax = 0 , vy = –9.8 m/s2
c.
d.
E. 1. a. No, b. No, c. yes, d. no. Velocity has a direction; the other three things do
not.
2. Refer back to quiz B for a step-by-step description of how I made this diagram.
Measuring the resultant’s length with a ruler and direction with a protractor gives:
R = 1.37 N,  = -15°