1. A volunteer firefighter holds the end of a fire hose as a strong jet of water
emerges. (a) The hose exerts a large backward force on the firefighter. Explain the
origin of this force. (b) If another firefighter steps on the hose, forming a
constriction
Four Equations for Constant ax
Each equation relates 4 of the 5 variables x, t, vix, vfx and ax
Problems give 3, ask for 4th (then 5th?)
One best equation for 4th, then choice of 2 for 5th
1. vfx vix = axt
2. x = (vfx+vix)t
3. x = vixt + ax(t)2
(Quadratic
Average acceleration aav,x vx/t
ax = slope of vx-t plot, rate of change of vx
ax positive, vx increasing (no info about vx)
ax = 0, vx = constant (ditto)
ax negative, vx decreasing (ditto)
Example of Finding ax
ax = slope of vx-t
= vx/t (m/s2)
With x and
1. You are walking to class with a backpack full of books. As you walk at constant
speed on flat ground, does the force exerted on the backpack by your back and
shoulders do any work? If so, is it positive or negative? Answer the same
questions in two oth
1. Explain why it is easier to drive a wood screw using a screwdriver with a large
diameter handle rather than one with a thin handle.
Two external forces influence the motion of the suspended irregular objectthe normal
force from the nail acting at its p
1. In the design of a roller coaster, is it possible for any hill of the ride to be higher
than the first one? If so, how?
Work is done on the roller coaster by a tow chain or some other mechanism designed to
increase its height with respect to the ground
1. A bungee jumper leaps from a bridge and comes to a stop a few centimeters
above the surface of the water below. At that lowest point, is the tension in the
bungee cord equal to the jumpers weight? Explain why or why not.
The tension in the bungee cord
1. A firecracker at rest explodes, sending fragments off in all directions. Initially
the firecracker has zero momentum, but after the explosion the fragments flying
off each have quite a lot of momentum. Hasnt momentum been created? If not,
explain why n
1. Two children ride on a merry-go-round. One is 2 m from the axis of rotation and
the other is 4 m from it. Which child has the larger (a) linear speed, (b)
acceleration, (c) angular speed, and (d) angular displacement?
The child farthest from the axis,
1. It is commonly said that wood floats because it is lighter than water or that a
stone sinks because it is heavier than water. Are these accurate statements? If
not, correct them
No, they are not lighter or heavier than water, they are just more or less