Homework
1. A 6.0-kg object undergoes an acceleration of 2.0 m/s2.
(a) What is the magnitude of the resultant force acting on
it? (b) If this same force is applied to a 4.0-kg object, what
acceleration is produced?
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Chapter 4, Laws of Motion
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2. A freight train has a mass of 1.5 X 107 kg. If the
locomotive can exert a constant pull of 7.5 X 105 N, how
long does it take to increase the speed of the train from rest
to 80 km/h?
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Chapter 4, Laws of Motion
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3. A boat moves through the water with two forces acting
on it. One is a 2,000-N forward push by the water on the
propeller, and the other is a 1,800-N resistive force due to
the water around the bow. (a) What is the acceleration of
the 1,000-kg boat? (b) If it starts from rest, how far will the
boat move in 10.0 s? (c) What will its velocity be at the end
of that time?
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Chapter 4, Laws of Motion
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4. Two blocks are fastened to the ceiling of an elevator as
in this figure; the mass of each is 5.0 kg. The elevator
accelerates upward to 2.0 m/s2. Find the tension in each
rope.
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5. The block in this figure has a mass of 5 kg. The
inclined plane has an angle of θ=30⁰. The coefficient of
static friction is 0.2; the coefficient of kinetic friction is 0.1.
What must Fup be in order for the block to remain in place?
If Fup=55 N, what is the acceleration of the block?
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Chapter 4, Laws of Motion
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6. This figure shows a block suspended by two ropes. The
ropes are attached to the ceiling at angles as shown. If the
mass of the block is 10 kg, what is the tension in the rope
on the left?
General Physics I
Chapter 4, Laws of Motion
Page 148
General Physics I
Chapter 4, Laws of Motion
Page 149
7. A dockworker loading crates on a ship finds that a 20-kg
crate, initially at rest on a horizontal surface, requires a 75N horizontal force to set it in motion. However, after the
crate is in motion, a horizontal force of 60 N is required to
keep it moving with a constant speed. Find the coefficients
of static and kinetic friction between crate and floor.
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Chapter 4, Laws of Motion
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8. A 1.25-kg object is moving in the x direction at 17.4 m/s.
Just 3.41s later, it is moving at 26.8 m/s at 34.0° to the x
axis. What are the magnitude and direction of the force
applied during this time? What is the force in vector
notation?
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Chapter 4, Laws of Motion
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9. A 2.0-kg mass and a 3.0-kg mass are on a horizontal
frictionless surface, connected by a massless spring with
spring constant k = 140 N/m. A 30-N force is applied to the
larger mass, as shown in this figure. How much does the
spring stretch from its equilibrium length? (The force
required to compress or stretch a spring is given by F=kx,
where F is the force and x is the displacement of the
spring.)
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Chapter 4, Laws of Motion
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10. Consider the previous problem. What is the elongation
of the spring if the kinetic frictional force between the floor
and each of the blocks is 0.2?
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Chapter 4, Laws of Motion
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