Since the ladder is standing, we know that the coefficient
of friction is at least something. This [gotta be at least this] friction
coefficient can be calculated. As the man begins to climb the ladder, the
friction can even be less than the free-standing friction coefficient. However,
as the man climbs the ladder, more and more friction is required. Since he
eventually slips, we know that friction is less than what's required at the top
of the ladder.
The only "answer" to this problem is putting lower
and upper bounds on the coefficient. For the lower one, find how much friction
the ladder needs to stand by itself. For the most that friction could be, find
what friction is when the man reaches the top of the ladder.
Ff = uN1
Fx = 0 = Ff + N2
Fy = 0 = N1 – 400 – 864
N1 = 1264 N
Torque balance
T = 0 = N2(12)sin(60) – 400(6)cos(60) – 864(7.8)cos(60)
N2 = 439 N
Ff = 439= u N1
U = 440 / 1264 = 0.3481
Answer: Internal energy changes that do not register on a thermometer are due to changes in the potential energy of the particles.
Explanation: a thermometer measures the temperature, which is a measure of the average kinetic energy of the particles.
Answer:
1/R = 1/R1 + 1/R2 + 1/R3
1/1 + 1/2 + 1/4 = 1 + .5 + .25 = 1.75
1/1.75 = .572
multiplying this by 100 gives us
R = 57.2 ohms
The smallest resistor (100 ohms) will draw the most current
(One can also use R = R1 R2 R3 / (R1 R2 + R1 R3 + R2 R3)
