Newton's first law of motion, or the law of inertia, states: "An object will continue in its state of motion
unless acted upon by a net outside force."

Alex was traveling to school when he had a little accident. First, Alex's skateboard got caught on a crack in the sidewalk, but Alex himself kept moving forward. Then, a startled passerby stopped directly in front of Alex. Finally, Alex collided with the passerby, coming to a rather painful stop. At which point was Alex himself acted on by a net outside force?
A.
when he collided with the passerby
B.
when the passerby stopped
C.
when the skateboard got caught on the sidewalk
D.
when he kept moving forward

Several students in the group made comments to the coach about the back pack. which student has the correct analysis of the forces and motion of the back pack?

According to the phase diagram for water, how is the state of water determined? proceed up a vertical line at any given temperature read the phase at the intersection of any given temperature and pressure at a given pressure, proceed horizontally to the s-l or l-g line

Part f - example: finding two forces (part i) two dimensional dynamics often involves solving for two unknown quantities in two separate equations describing the total force. the block in (figure 1) has a mass m=10kg and is being pulled by a force f on a table with coefficient of static friction îľs=0.3. four forces act on it: the applied force f (directed î¸=30â above the horizontal). the force of gravity fg=mg (directly down, where g=9.8m/s2). the normal force n (directly up). the force of static friction fs (directly left, opposing any potential motion). if we want to find the size of the force necessary to just barely overcome static friction (in which case fs=îľsn), we use the condition that the sum of the forces in both directions must be 0. using some basic trigonometry, we can write this condition out for the forces in both the horizontal and vertical directions, respectively, as: fcosî¸â’îľsn=0 fsinî¸+nâ’mg=0 in order to find the magnitude of force f, we have to solve a system of two equations with both f and the normal force n unknown. use the methods we have learned to find an expression for f in terms of m, g, î¸, and îľs (no n).