COLLEGE PHYSICS
13th Edition
ISBN: 2810014673880
Author: OpenStax
Publisher: OpenStax
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Chapter 7, Problem 21PE
In a downhill ski race, surprisingly, little advantage is gained by getting a running start. (This is because the initial kinetic energy is small compared with the gain in gravitational potential energy on even small hills.) To demonstrate this, find the final speed and the time taken for a skier who skies 70.0 m along a 30° slope neglecting friction: (a) Starting from rest. (b) Starting with an initial speed of 2.50 m/s. (c) Does the answer surprise you? Discuss why it is still advantageous to get a running start in very competitive events.
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A 1.40-kg object slides to the right on a surface having a coefficient of kinetic friction 0.250 (Figure a). The object has a speed of v₁ = 3.50 m/s when it makes contact with a light spring (Figure b) that has a force constant of 50.0 N/m. The object comes to rest after the spring has been
compressed a distance d (Figure c). The object is then forced toward the left by the spring (Figure d) and continues to move in that direction beyond the spring's unstretched position. Finally, the object comes to rest a distance D to the left of the unstretched spring (Figure e).
d
m
v=0
-D- www
(a) Find the distance of compression d (in m).
m
(b) Find the speed v (in m/s) at the unstretched position when the object is moving to the left (Figure d).
m/s
(c) Find the distance D (in m) where the object comes to rest.
m
(d) What If? If the object becomes attached securely to the end of the spring when it makes contact, what is the new value of the distance D (in m) at which the object will come to…
As shown in the figure, a 0.580 kg object is pushed against a horizontal spring of negligible mass until the spring is compressed a distance x. The force constant of the spring is 450 N/m. When it is released, the object travels along a frictionless, horizontal surface to point A, the bottom of a
vertical circular track of radius R = 1.00 m, and continues to move up the track. The speed of the object at the bottom of the track is VA = 13.0 m/s, and the object experiences an average frictional force of 7.00 N while sliding up the track.
R
(a) What is x?
m
A
(b) If the object were to reach the top of the track, what would be its speed (in m/s) at that point?
m/s
(c) Does the object actually reach the top of the track, or does it fall off before reaching the top?
O reaches the top of the track
O falls off before reaching the top
○ not enough information to tell
A block of mass 1.4 kg is attached to a horizontal spring that has a force constant 900 N/m as shown in the figure below. The spring is compressed 2.0 cm and is then released from rest.
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x = 0
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(a) A constant friction force of 4.4 N retards the block's motion from the moment it is released. Using an energy approach, find the position x of the block at which its speed is a maximum.
ст
(b) Explore the effect of an increased friction force of 13.0 N. At what position of the block does its maximum speed occur in this situation?
cm
Chapter 7 Solutions
COLLEGE PHYSICS
Ch. 7 - Give an example of something think of as work in...Ch. 7 - Give an example of a situation in which there is a...Ch. 7 - Describe a situation in which a force is exerted...Ch. 7 - The person in Figure 7.33 does work on the lawn...Ch. 7 - Work done on a system puts energy into it Work...Ch. 7 - When solving for speed in Example 7.4, we kept...Ch. 7 - In Example 7.7, we calculated the final speed of a...Ch. 7 - Does the work you do on a book when you lift it...Ch. 7 - What is a conservative force?Ch. 7 - The force exerted by a diving board is...
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