# How fast is Dale Earnhart�s car moving? by 18EV0q9

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```									How fast is Dale Earnhart’s car moving?
Pizza delivery: need Osama’s GPS
coordinates
A window washer on a scaffold is hoisting the scaffold up the side of a
building by pulling downward on a rope, as shown here. If the magnitude of
the pulling force is 540 N and the combined mass of the worker and the
scaffold combination is 155 kg, how long will it take him to move up by 5 m?
Can Robin Hood escape?
The drawing shows Robin Hood (mass =
82 kg) about to escape from a dangerous
situation. With one hand, he is gripping
the rope that holds up a chandelier (mass
= 220 kg). When he cuts the rope where
it is tied to the floor, the chandelier will
fall, and he will be pulled up toward a
balcony above. Ignoring the friction
between the rope and the beams over
which it slides, calculate the time it takes
for him to rise by 4 meters to the balcony
above.
A monkey clinging to one end of a rope
that passes over a frictionless pulley is
balanced by a mirror of exactly equal
weight on the other end of the rope.
Can the monkey climb up or down to
escape the image?
The figure shows a section of an
airplane cable-car system. The
maximum permissible mass of each car
with occupants is 2900 kg. The cars,
riding on a support cable, are pulled by
a second cable attached to each pylon
(support tower); assume the cables are
straight. What is the difference in
pull cable if the cars at the maximum
permissible mass and are being
accelerated up the 35° incline at 0.83
m/s2?
A student from Physics 201 finds that her car is stuck in the sand and
cannot be driven out. Unable to push it out, she ties a strong rope from
the front of the car to a large tree 26 m away and directly in front of the
car. She then pushes on the middle of the rope with a force of 425 N in a
direction perpendicular to the length of the rope. If the midpoint of the
rope is displaced by 1 m, what is the force applied to the car?
Can the rope ever be perfectly
horizontal?
The tension at which a fishing line snaps is commonly called
the line's "strength.“ Assuming a constant deceleration, what
minimum strength is needed for a line that is to stop a salmon
of weight 85 N in 8.8 cm if the fish is initially drifting at 2.9
m/s?
The Gagarin Cosmonaut Training Center is used to train
Russian cosmonauts for space missions. If the device can
rotate at 36 rpm and has a radius of rotation of about 20 m,
what acceleration does the trainee experience?
Tarzan plans to cross a gorge by
swinging in an arc from a hanging
vine. If his arms are capable of
exerting a force of 1100 N on the
rope, what is the maximum speed
he can tolerate at the lowest point
of his swing? His mass is 70 kg
and the vine is 4.8 m long.
CAUTION - DANGEROUS CURVE AHEAD - REDUCE
SPEED TO 20 MPH

Johnny gauged the coefficient of friction between his tires and the road to be
0.40. Calling on his extensive knowledge of physics and his skepticism of truth
in advertising, he figured that the sign was there to scare, not to protect, and
that he could easily take the turn at 30 mph, a full 10 mph above the posted
speed limit. The turn was a tight one, 50 meters in radius.
1. Did Johnny make it?
2. How far below the true speed limit was the posted speed limit?
3. If there were no friction, the turn would have to be banked. Find the
necessary angle for this banking, in order for Johnny to complete the turn at
the same maximum speed as friction allowed.
The set-up
A daredevil stunt involves riding a motorcycle around the
vertical inside wall of a cylindrical structure. If the cylinder
has a radius of 15 m and the coefficient of static friction
between the motorcycle tires and the wall is 1.1, what is the
minimum speed that will keep the motorcycle and the rider
from sliding down the wall?
Secret to success
End
A crate starts from rest and slides 8.15 m down a ramp. When
it reaches the bottom it is traveling at a speed of 5.75 m/s. If
the ramp makes an angle of 22.0° with the horizontal, what is
the coefficient of friction between the crate and the ramp?
Applet: Incline with friction
CAUTION - DANGEROUS CURVE AHEAD - REDUCE
SPEED TO 20 MPH

Johnny gauged the coefficient of friction between his tires and the road to be
0.40. Calling on his extensive knowledge of physics and his skepticism of truth
in advertising, he figured that the sign was there to scare, not to protect, and
that he could easily take the turn at 30 mph, a full 10 mph above the posted
speed limit. The turn was a tight one, 50 meters in radius.
1. Did Johnny make it?
2. How far below the true speed limit was the posted speed limit?
3. If there were no friction, the turn would have to be banked. Find the
necessary angle for this banking, in order for Johnny to complete the turn at
the same maximum speed as friction allowed.
What angle requires the
smallest tension force in
overcoming static friction?
A circus clown weighing 890 N pulls
vertically downward on a rope that
passes around three pulleys and is tied
around his feet. If the coefficient of
static friction between the clown's feet
and the ground is 0.53, what is the
minimum pulling force that the clown
must exert to yank his feet out from
under himself?
End
A fish of mass m is suspended by
a string as shown. The string is
fastened securely at point C but
will pull loose from the wall at A
when the string tension exceeds
19 N. What is the maximum mass
of the fish that can be supported
by the string?
Suppose that the coefficient of static
friction ms between the rider's clothing
and the canvas is 0.40 and that the
cylinder's radius R is 2.1 m. What
minimum speed v must the cylinder
and rider have if the rider is not to fall
when the floor drops?
Suppose two horses pull horizontally, each with a force F, on
ropes attached to a tree stump. If the angle between the two
ropes is 110°, what is the resultant force?
A crate starts from rest and slides 8.15 m down a ramp. When
it reaches the bottom it is traveling at a speed of 5.75 m/s. If
the ramp makes an angle of 22.0° with the horizontal, what is
the coefficient of friction between the crate and the ramp?
A 6-kg monkey climbs up a massless
rope that runs over a frictionless tree
limb and back down to a 23-kg
package on the ground. How long will
it take the monkey to reach the branch
4 m above the ground if it is able to
just barely lift the package off the
ground?

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