WEBASSIGN 24 PRACTICE PROBLEMS
NAME_______________________
1. - Question Details energy symbolic spring mass 2 [2141241]
A block of mass m is attached to a horizontal spring of constant K as shown below. Position B indicates the
unstretched length of the spring; the spring is initially compressed a distance x A from its unstretched length,
and the mass is then released from rest. The floor has coefficient of friction μ.
Write expressions for the quantities listed in the left column; note that this refers to points A and B in the
diagram.
Use the following as necessary: vB, m, xA, μ, g, K
Total Energy at A
Positive Work Done (A to B)
Negative Work Done (A to B)
Total Energy at B
Now write the energy conservation equation between points A and B:
=
Solve for the mass of the block. Use the following as necessary: vB, xA, μ, g, K
m=
2. Question Details Energy spring mass horizontal 2 [1698323]
A mass of 0.612 kg is attached to a horizontal spring of constant 367 N/m as shown. The system is
compressed a distance xa = 21.4 cm from its equilibrium position and released from rest. The coefficient of
friction on the surface is μ = 0.367. The mass comes to rest again at some distance xc on the other side of
the equilibrium position.
A. What is the elastic potential energy at point A?
B. What is the deformation of the spring at point C?
8.40 J
0.202 m
C. What is the work done by friction between points A and C?
D. What is the velocity of the mass at point B?
-0.916 J
5.09 m/s
3. - Question Details energy symbolic Atwood A 2 [2181181]
The Atwood machine shown below consists of differential masses connected with a string over a massless,
frictionless pulley (m2 > m1). The system is released from rest at point A where each mass is at a height H
above the floor; point B is as m2 hits the floor.
Write expressions for the quantities listed in the left column.
Use the following as necessary: m1, m2, g, H, vB
Total Energy at A
Positive Work Done
Negative Work Done
Total Energy at B
Now write the energy conservation equation:
=
Solve for the height H of the system at point A. Use the following as necessary: g, v B, m1, m2
H=
4. - Question Details Energy Atwood 1 [1697134]
An Atwood machine consists of two masses (m1 = 120 grams, m2 = 460 grams) connected by a string over
a frictionless pulley. The initial height above the floor is 163 cm. Both masses start from rest at point A in
the position shown; point B is just as m2 hits the floor.
A. What is the gravitational potential energy of m1 at point A?
1.92 J
B. What is the gravitational potential energy of m2 at point A?
7.35 J
C. What is the kinetic energy of the system at point A?
0.00 J
D. What is the gravitational potential energy of m1 at point B?
3.83 J
E. What is the gravitational potential energy of m2 at point B?
0.00 J
F. What is the kinetic energy of the system at point B?
G. What is the velocity of the system at point B?
4.33 m/s
H. What is the kinetic energy of m1 at point B?
I. What is the kinetic energy of m2 at point B?
5.43 J
1.12 J
4.31 J
5. - Question Details energy symbolic cart mass 2 [2172584]
The system shown below consists of a cart (mass m1) attached by a string to a hanging mass (m2). The desk
is at a height H1 above the floor, and its surface has coefficient of friction μ. The hanging mass m2 begins at
a height H2 above the floor. The system is released from rest as shown at point A, and point B is just as m 2
hits the floor.
Write expressions for the quantities listed in the left column. Use the following as necessary: m 1, m2, H1,
H2, μ, vB, g
Total Energy at A
Positive Work Done
Negative Work Done
Total Energy at B
Now write the energy conservation equation:
=
Solve for the coefficient of friction μ on the desk. Use the following as necessary: m1, m2, vB, g, H2
μ=
6. - Question Details Energy Cart-mass 2 [1700444]
A cart-mass system consists of a cart of mass 485 grams connected by a string over a frictionless pulley to
a hanging mass of 132 grams. The system starts from rest, and the lab desktop is 175 cm above the floor,
while the hanging mass starts 75.0 cm above the floor. When m2 hits the floor, it is moving with a velocity
of 1.02 m/s. As shown in the diagram is point A, and point B is when mass m 2 hits the floor.
A. What is the total mechanical energy in the system at point A?
B. What is the kinetic energy of the system at point B?
0.318 J
C. What is the work done by friction between points A and B?
D. What is the coefficient of friction on the desktop?
9.29 J
-0.652 J
0.183
7. - Question Details energy symbolic bungee 2 [2443946]
A guy of mass m stands at rest on a platform of height H with a bungee cord attached to his leg (point A).
The bungee cord has an unstretched length of L0 and spring constant K. The guy drops over the side and is
in free-fall for a brief time, until the bungee cord begins to stretch (at point B). The bungee cord stretches
out, until the guy stops briefly at a height of HC above the ground (point C).
Write expressions for the quantities listed in the left column. Note that this problem refers to points A and
C.
Use the following as necessary: xC, HC, m, H, g, K
Total Energy at A
Positive Work Done
Negative Work Done
Total Energy at C
Now write the energy conservation equation:
=
Solve for the unstretched length of the bungee cord L0. Use the following as necessary: xC, g, m, K
HINT: First find HC in terms of H, L0, and xC.
L0 =
8. - Question Details energy symbolic bungee 7 [2444214]
A guy of mass m stands at rest on a platform of height H with a bungee cord attached to his leg (point A).
The bungee cord has an unstretched length of L0 and spring constant K. The guy drops over the side and is
in free-fall for a brief time, until the bungee cord begins to stretch (at point B). The bungee cord stretches
out, until the guy stops briefly at a height of HC above the ground (point C).
Write expressions for the quantities listed in the left column. Note that this problem refers to points B and
C.
Use the following as necessary: xC, HC, m, HB, vB, g, K
Total Energy at B
Positive Work Done
Negative Work Done
Total Energy at C
Now write the energy conservation equation:
=
Solve for the mass of the guy. Use the following as necessary: xC, g, K, vB
HINT: First find HC and HB in terms of H, L0, and xC.
m=
9. - Question Details Energy bungee 1 [1700368]
A guy of mass 61.2 kg stands at rest on a platform of height 286 m with a bungee cord attached to his leg
(point A). The bungee cord has an unstretched length of 32.3 m. The guy drops over the side and is in freefall for a brief time, until the bungee cord begins to stretch (at point B). The bungee cord stretches out, until
the guy stops briefly at a height of 11.2 m above the ground (point C).
A. What is the GPE at point A?
B. What is the KE at point A?
1.72e+05 J
0.00 J
C. What is the EPE at point A?
0.00 J
D. What is the GPE at point B?
1.52e+05 J
E. What is the KE at point B?
19400 J
F. What is the EPE at point B?
0.00 J
G. What is the guy's velocity at point B?
H. What is the GPE at point C?
25.2 m/s
6720 J
I. What is the KE at point C?
J. What is the EPE at point C? 1.65e+05 J
K. What is the spring deformation at point C? 243 m
0.00 J
L. What is the spring constant of the spring?
5.61 N/m
M. What is the spring force acting on the guy at point C?
1360 N