* Your friend has a pie on the roof of his van. You are standing on the ground and observe the van stopping abruptly for a red light. The pie does not slip off the roof. (a) Construct a motion diagram and a force diagram for the pie as the van approaches the red light, from your frame of reference and from the driver's frame of reference. (b) Repeat part (a) for the case when the light turns green. Be sure to specify the observer and identify the other object causing each force. (c) Are the motion diagrams consistent with the force diagrams for each case?
* Your friend has a pie on the roof of his van. You are standing on the ground and observe the van stopping abruptly for a red light. The pie does not slip off the roof. (a) Construct a motion diagram and a force diagram for the pie as the van approaches the red light, from your frame of reference and from the driver's frame of reference. (b) Repeat part (a) for the case when the light turns green. Be sure to specify the observer and identify the other object causing each force. (c) Are the motion diagrams consistent with the force diagrams for each case?
* Your friend has a pie on the roof of his van. You are standing on the ground and observe the van stopping abruptly for a red light. The pie does not slip off the roof. (a) Construct a motion diagram and a force diagram for the pie as the van approaches the red light, from your frame of reference and from the driver's frame of reference. (b) Repeat part (a) for the case when the light turns green. Be sure to specify the observer and identify the other object causing each force. (c) Are the motion diagrams consistent with the force diagrams for each case?
A 15.0 kg load of bricks hangs from one end of a rope that passes
over a small, frictionless pulley. A 28.0 kg counter weight is
attached to the other end of the rope, as shown in the figure. You
may model the rope as a massless string. The system is released
from rest.
A. Draw two freebody diagrams, one for the load of bricks and
one for the counter weight.
B. Find the magnitude of the upward acceleration of the load
of bricks.
28.0 kg
C. What is the tension in the rope?
D. How does the tension compare to the weight of the bricks
and the weight of the counter weight?
15.0 kg
A person places a cup of coffee on the roof of her car while she dashes back
into the house for a forgotten item. When she returns to the car, she hops in
and takes off with the coffee cup still on the roof. You may want to review
(Pages 156 - 163).
Part A
If the coefficient of static friction between the coffee cup and the roof of the car is 0.21, what is the maximum acceleration the car can have without causing the cup to slide? Ignore the effects of
air resistance.
Express your answer using two significant figures.
a =
m/s?
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• Part B
What is the smallest amount of time in which the person can accelerate the car from rest to 27 m/s and still keep the coffee cup on the roof?
Express your answer using two significant figures.
ΑΣφ.
t =
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Piles of snow on slippery roofs can become dangerous projectiles as they melt. Consider a chunk of snow at the ridge of a roof with a slope of 32 degrees.
a.) What is the minimum value of the coefficient of static friction that will keep the snow from sliding down?
Express your answer using two significant figures.
b.) As the snow begins to melt, the coefficient of static friction decreases and the snow finally slips. Assuming that the distance from the chunk to the edge of the roof is 5.0 m and the coefficient of kinetic friction is 0.10, calculate the speed of the snow chunk when it slides off the roof.
Express your answer to two significant figures and include the appropriate units.
c.) f the roof edge is 12.5 m above ground, estimate the speed of the snow when it hits the ground.
Express your answer to two significant figures and include the appropriate units.
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