Question

7. An aluminum wire 1.0 m in length and 2.0 mm in diameter supports a 10.0-kg mass. What is the elongation of the wire? (The Young's modulus for an aluminum is 7.0 × 1010 N/m2)

3. Two equal forces are applied to a door. The first force is applied at the midpoint of the door; the second force is applied at the doorknob. Both forces are applied perpendicular to the door. Which force exerts the less torque?

Answer #1

Solution :

(7)

(3) The hinge is the axis of rotation in both cases.

Now, the midpoint of the door is closer to the hinge compared to the doorknob.

Also, torque is directly propotional between the distance of point of application of force and the axis of rotation.

Hence, the first force will produce less torque, since it is applied closer to the axis of rotation.

A student is testing a 1.0 m length of 2.0-mm-diameter steel
wire.
Part A How much force is required to stretch this wire by 1.0
mm? Young's modulus for steel is 20×1010N/m2. Express your answer
to two significant figures and include the appropriate units.
F=
Part B What length of 4.0-mm-diameter wire would be stretched by
1.0 mm by this force? Express your answer to two significant
figures and include the appropriate units.
L2 =

A metal wire 1.0 m long and of 2.0 mm diameter is stretched by a
load of 40.0 kg. the extension produced on the wire is 1.5mm.
What is the stress?
What is the strain?
Young's modulus of elasticity?
The energy stored in the Wire.
The Force constant

A wire of diameter 1.0 mm and length 3.5 m stretches 3.5 mm when
8.0 kg is hung from it.
a) What is the Young's modulus for the wire?
b) What is the effective spring constant for the stretching
wire?

Calculate the ratio of the resistance of 9.4 m of aluminum wire
2.0 mm in diameter, to 15.7 m of copper wire 2.4 mm in diameter.
RAl / RCu = 1.33 Incorrect: Your answer is incorrect.

Consider a straight piece of copper wire of length 7 m and
diameter 3.5 mm that carries a current I = 5.5 A. There is a
magnetic field of magnitude B directed perpendicular to the wire,
and the magnetic force on the wire is just strong enough to
“levitate” the wire (i.e., the magnetic force on the wire is equal
to its weight). Find B. Hint: The density of copper is 9000
kg/m3 .

Consider a straight piece of copper wire of length 2 m and
diameter 8.5 mm that carries a current I = 9 A. There is a magnetic
field of magnitude B directed perpendicular to the wire, and the
magnetic force on the wire is just strong enough to “levitate” the
wire (i.e., the magnetic force on the wire is equal to its weight).
Find B. Hint: The density of copper is 9000 kg/m3 .

Materials lectures:
1- A wire 0.00108 m in diameter and 1.5 m in length is used to
support a load of 37 kg. The wire increases in length by 0.00088 m.
To 3 significant figures, what is Young's Modulus of the wire in SI
units of force per area? (answer: 6.75e11 N/m^2)
2- The atmospheric pressure above a fresh water lake is 101.2
kPa. What is the pressure in pascals at 12.1 m below the surface?
(answer: 2.20e5 Pa)
3-...

(a) A 34.7-m length of copper wire at 20.0°C has a radius of
0.29 mm. If a potential difference of 7.0 V is applied across the
length of the wire, determine the current in the wire. (Use the
values in the following table.)
Resistivities and Temperature Coefficients of Resistivity
for Various Materials (at 20°C)
Material
Resistivity
(Ω · m)
Temperature
Coefficient
of Resistivity [(°C)−1]
Silver
1.59 ✕ 10−8
3.8 ✕ 10−3
Copper
1.7 ✕ 10−8
3.9 ✕ 10−3
Gold
2.44...

(a) A 35.1-m length of copper wire at 20.0°C has a radius of
0.31 mm. If a potential difference of 7.0 V is applied across the
length of the wire, determine the current in the wire. (Use the
values in the following table.)
Resistivities and Temperature Coefficients of Resistivity
for Various Materials (at 20°C)
Material
Resistivity
(Ω · m)
Temperature Coefficient
of Resistivity [(°C)−1]
Silver
1.59 ✕ 10−8
3.8 ✕ 10−3
Copper
1.7 ✕ 10−8
3.9 ✕ 10−3
Gold
2.44...

1. A cord of mass 0.65 kg is stretched between two supports 8.0
m apart. If the tension in the cord is 140 N, how long will it take
a pulse to travel from one support to the other?
2. A 50.0 Kg ball hangs from a steel wire 1.00 mm in diameter
and 6.00 m long. What would be the speed of a wave in the steel
wire?
3. The intensity of an earthquake wave passing through the earth...

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