Review 5 kg 7 m/s

Review
Dr. Bennett throws a 2.7 kg brick directly upward at
15.0 m/s from ground level. How high will the brick
be when its speed has been reduced to half of its
initial value. Assume the brick loses 5% of its initial
kinetic energy to air resistance.
A 12.0-kg rock is subject to a variable force
given by the equation
6.0 2.0 /
If the rock initially is at rest at the origin, find its
speed when it has moved 9.0 m.
EF 151 Fall, 2014 Lecture 3-8
1
A 5.0-kg block is moving at 7.0 m/s along a horizontal frictionless
surface toward a spring that is attached to a wall. After the block collides
with the spring, the spring is compressed a maximum distance of 0.68
m. What is the speed of the block when the spring is compressed to only
one-half of the maximum distance?
EF 151 Fall, 2014 Lecture 3-8
2
A crane is used to raise a 89-kg crate vertically
upward. If the power output of the engine is
1620 W, how long does it take the engine to lift
the crate a vertical distance of 18.7 m?
7 m/s
5 kg
EF 151 Fall, 2014 Lecture 3-8
3
EF 151 Fall, 2014 Lecture 3-8
4
A particle of mass 4.12×10-27 kg, moving at 4.62×105
m/s, strikes an identical particle which is initially at rest.
After the interaction, the particles (which can't be
distinguished) are observed moving at angles 55.3° and
-34.7°, both angles being measured with respect to the
original direction of motion. What are the final speeds
of the particles?
A 1000 kg roller coaster descends 35 meters in its
initial drop and then rises 23 meters. The speed at this
point is 7 m/s. How much energy was lost if its initial
speed was 2 m/s?
EF 151 Fall, 2014 Lecture 3-8
5
6
Two bowling balls collide as shown. The coefficient of restitution between
the balls is 0.80. What is the velocity of the 12 lb ball after the collision?
A 10.0-kg shell is traveling horizontally to the right at 25.0 m/s relative to
the ground when it explodes into two fragments, one of mass 3.00 kg
and the other of mass 7.00 kg. The lighter fragment goes directly
forward, and the explosion releases 1.50 × 103 J of mechanical energy to
the fragments. Find the magnitude and direction of the velocity of the
heavier fragment relative to the ground just after the explosion.
EF 151 Fall, 2014 Lecture 3-8
EF 151 Fall, 2014 Lecture 3-8
vA= (20i – 7j) ft/s
WA = 12 lb
A
7
EF 151 Fall, 2014 Lecture 3-8
y
B
vB= (–15i – 10j) ft/s
WB = 16 lb
x
8

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