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Type: Double
Date: ____________
Objective: Work and Energy Conservation I
Work and Energy Conservation II
Homework: Assignment (1-27)
Do PROBS # (38, 55) Ch. 6 + PROBS # (8) Ch. 10
AP Physics “B”
Mr. Mirro
Date:
Work and Energy Conservation I
________
Ex 1: A 755 N diver drops from a platform 10.0 m above the water surface, as shown. [Serway5.4]
a. Use conservation of mechanical energy to find his speed 5.0 m
above the surface of the water.
h = 5m
b. Find the speed of the diver just before
he strikes the water.
Ex 2: The spring constant for a spring in a dart gun is 1400 N/m. When the gun is cocked, the spring
is compressed by 0.075 m. If the gun is shot vertically upward, neglecting air resistance
[Cutnell4EP50mod]
a. What is the speed of a 2.4 x 10-2 kg dart when it leaves the gun ?
b. Determine the maximum height of the dart.
Ex 3: A sled and its rider together weigh 800 N. They (the sled-rider system) move down a frictionless
hill through a vertical distance of 10 m as shown. Use conservation of mechanical energy to find
the speed of the sled-rider system at the bottom of the hill, assuming the rider pushes off with an
initial speed of 5.0 m/s. [Serway5.5]
vi = 5 m/s
10 m
θ
0m
Ex 4: A 1 kg sphere (M), suspended by a string from point (P), is lifted to a height (h). The sphere is
released and passes through the lowest point in its swing at a speed (v) of 10 m/s. [General]
a. Determine the height from which the sphere
was released.
P
M
h
M
Δx
b. If the constant of elasticity for the spring is 1600 N/m, how much will the spring compress
upon impact ?
AP Physics “B”
Mr. Mirro
Date:
________
Work and Energy Conservation II
Ex 1: A horizontal spring having a spring constant k = 360 N/m is lying on a frictionless surface. One
end of the spring is attached to a wall, and the other end is connected to a mass of m = 2.8 kg. The
spring is then compressed by 0.065 m and released from rest. [Cutnell4EP48]
a. Using conservation of energy, determine the expression for
the speed at any position in terms of k, x and m only.
xf = .048 m
stretch
xi = .065 m
Eq
compress
b. What is the speed of the object at the instant when the
spring is stretched by 0.048 m relative to its unstrained
length ?
c. Compute the maximum speed, veq, of the mass at the
instant it crosses the equilibrium point.
Ex 2: A rifle fires a 2.2 x 10-2 kg pellet straight upward, because the pellet rests on a compressed spring
that is released when the trigger is pulled. The spring has a negligible mass and is compressed by
9.5 x 10-2 m from its unstrained length. The pellet rises to a maximum height of 7.0 m above its
position on the compressed spring. Ignoring air resistance, determine the spring constant.
[Cutnell4EP52]
Ex 3: Assuming the height of the first hill in a roller coaster is h1 = 50 m. A roller coaster proceeds to
gain speed as it goes through several dips. At the end of the last dip there is an elastic protection
device (EPD) that has an elastic constant of 20000 N/m. If the roller coaster car has mass m = 10
kg and the car essentially starts from rest at the top of the first hill, determine the following
information about the motion of the roller coaster car: [Cutnell6.7sim]
A
B
50 m
C
60
m
E
20 m
D
vf (comp)
=0
a. Find the potential energy due to gravity, translational kinetic energy, elastic potential energy and
total
mechanical energy for the situation depicted above. NO WORK necessary for this section !
Position
PEg [J]
KE [J]
PES [J]
Total “ME” [J]
A
B
C
D
E
b. What is the velocity of the car at position D ?
c. How much does the “EPD” compress as the car is brought momentarily to rest ?