B2-WWT07:
The student’s contention is wrong since he/she took the differences in the magnitudes of the
velocities rather than the actual velocity differences for the interval. The acceleration for boat A
will be directed at some angle to the northwest and will have a magnitude of 2.5m/s2 (the length
of the v vector, since it is the hypotenuse of a 3-4-5 right triangle) divided by 10 s, giving
2.5m/s2. Boat B’s acceleration is directed eastward and has a magnitude of 5 m/s divided by 10
s, giving 0.5m/s2.
B2-WWT08
The horizontal velocity graphs need to be switched, because Rock A has no horizontal velocity,
and Rock B has a constant horizontal velocity. The vertical graph for Rock B is correct for both
rocks.
B2-QRT09
Since the positive horizontal direction is to the right, the horizontal velocity will be negative.
Since up is the positive vertical direction the ball has a positive initial vertical velocity, which
decreases to zero and then becomes negative.
Since there is no force in the horizontal direction there will be no horizontal acceleration. The
vertical acceleration is negative and equal in magnitude to g.