Page 88 - Schaum's Outline of Theory and Problems of Applied Physics

CHAP. 6] FRICTION 73

6.10. A car with its brakes locked will remain stationary on an inclined plane of dry concrete when the plane is at an angle
of less than 45 with the horizontal. What is the coefficient of static friction of rubber tires on dry concrete?
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6.11. A steel ramp is to be built for sliding blocks of ice from a refrigeration plant down to ground level. If µ = 0.05, find
the angle with the horizontal at which the ice will slide at constant velocity.

6.12. A box slides down a plane 8 m long that is inclined at an angle of 30 with the horizontal. If the box starts from rest
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and µ = 0.25, find (a) the acceleration of the box, (b) its velocity at the bottom of the plane, and (c) the time required
for it to reach the bottom.

6.13. If the box of Prob. 6.10 has a mass of 60 kg, how much force is needed to move it up the plane (a) at constant velocity
2
and (b) with an acceleration of 2 m/s ?
6.14. A skier stands on a 5 slope. If the coefficient of static friction is 0.1, does the skier start to slide down?
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Answers to Multiple-Choice Questions

6.1. (c) 6.6. (c)
6.2. (a), (c), (d ) 6.7. (a)

6.3. (d ) 6.8. (d )

6.4. (a) 6.9. (a)
6.5. (b) 6.10. (b)

Answers to Supplementary Problems

6.1. No. The frictional force that prevents the ship from sliding down the ways increases in proportion as the ship’s weight
increases.

6.2. Yes; no 6.9. 5.67 s

6.3. 40 lb 6.10. 1.0
6.4. 0.306 6.11. 3 ◦

6.5. 0.44 m/s 2 6.12. (a) 2.78 m/s 2 (b) 6.67 m/s (c) 2.40 s

6.6. 0.98 m/s 2 6.13. (a) 421 N (b) 541 N
6.7. 0.36 6.14. No

6.8. 18 m/s = 65 km/h