Chapter 7
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(p.174 prob.63) A 6.0-kg block is pushed 7.0m up a rough 37° inclined plane by a horizontal
force of 75N. If the initial speed of the block is 2.2m/s up the plane and a
constant kinetic friction force of 25N opposes the motion, calculate (a)
the initial kinetic energy of the block; (b) the work done by the 75-N
force; (c) the work done by the friction force; (d) the work done
by gravity; (e) the work done by the normal force; (f) the final
kinetic energy of the block.
Answer.
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(p.175 prob.67) A force F = (10.0i + 9.0j + 12.0k)kN
acts on a small object of mass 100g. If the displacement of the object is d
= (5.0i + 4.0j)m, find the work done by the force. What is the
angle between F and d?
Answer.
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(p.175 prob.70) The force required to compress an imperfect horizontal spring an
amount x is given by F = 150x + 12x2,
where x is in meters and F in newtons. If the spring is compressed
2.0m, what speed will it give to a 3.0-kg ball held against it and then
released?
Answer.
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(p.175 prob.75) Assume a cyclist of weight mg can exert a force on
the pedals equal to 0.90mg on the average. If the pedals rotate in a
circle of radius 18cm, the wheels have a radius of 34cm, and the front and back
sprockets on which the chain runs have 42 and 19 teeth respectively (Fig. 7-32),
determine the maximum steepness of hill the cyclist can climb at constant speed.
Assume the mass of the bike is 12kg and that of the rider is 60kg. Ignore
friction. Assume the cyclist's average force is always: (a) downward; (b)
tangential to pedal motion
Answer.
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