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3 years ago

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72.0-kg person pushes on a small doorknob with a force of 5.00 N perpendicular to the surface of the door. The doorknob is locat

ed 0.800 m from axis of the frictionless hinges of the door. The door begins to rotate with an angular acceleration of 2.00 rad/s2. What is the moment of inertia of the door about the hinges?

1 answer:

expeople1 [14]3 years ago

4 0

Answer: $I=2 kg-m^2$

Explanation:

Given

mass $m=72 kg$

Force $F=5 N$

door knob is located at a distance of r=0.8 m from axis

Angular acceleration of door $\alpha =2 rad/s^2$

Torque $T=I\alpha =F\times r$

where I=moment of inertia

$5\times 0.8=I\times 2$

$I=2 kg-m^2$

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A 5.00 kg rock whose density is 4300 kg/m3 is suspended by a string such that half of the rock's volume is under water. You may

12345 [234]

Answer:

The tension on the string is $T = 43.302 \ N$

Explanation:

From the question we are told that

The mass of the rock is $m_r = 5.00 \ kg = 5000 \ g$

The density of the rock is $\rho = 4300 \ kg/m^3 = 4.3 g/dm^3$

Generally the volume of the rock is mathematically evaluated as

$V = \frac{m_r}{\rho}$

substituting values

$V = \frac{5000}{4.3}$

$V = 1162.7 \ dm^3$

The volume of the rock immersed in water is

$V_w = \frac{V}{2}$

substituting values

$V_w = \frac{1162.7 }{2}$

$V_w = 581.4 \ dm^3$

mass of water been displaced by the this volume is

$m_w = V_w$ According to Archimedes principle

=> $m_w = 581.4 \ g$

$m_w = 0.5814 \ kg$

The weight of the water displace is

$W _w = m_w * g$

$W _w = 0.5814 * 9.8$

$W _w = 5.698 \ N$

The actual weight of the rock is

$W_r = m_r * g$

$W_r = 5.0 * 9.8$

$W_r = 49.0 \ N$

The tension on the string is

$T = W_r - W_w$

substituting values

$T = 49.0 - 5.698$

$T = 43.302 \ N$

4 0

3 years ago

A large refrigerator (mass 80kg) sits at rest inside a house. The homeowner wants to move the refrigerator across the room, so s

Liono4ka [1.6K]

Answer:

400 N

Explanation:

By the law of friction,

$F=\mu R$

$F$ is the maximum frictional force, $\mu$ is the coefficient of friction and $R$ is the reaction on the refrigerator. On a horizontal surface, the reaction is equal to the weight of the refrigerator.

$R=mg$

$F=\mu mg$

While not moving, the fricition on the refrigerator is static friction. So, $\mu=0.65$

$F=0.65 \times80\times9.8=509.6 \text{ N}$

This is the maximum frictional force and is more than the applied horizontal force of 400 N. Frictional force cannot be more than the applied force, else it would actually pull the refrigerator backwards (a strange thing, if it were to happen). It is equal to the extent of the applied force because the applied force is not enough to overcome the maximum.

Hence the frictional force is 400 N.

PS: Note that we do not use the coefficient of kinetic friction because applied force could not overcome the static friction.

6 0

3 years ago

Two resistors have resistances R(smaller) and R(larger), where R(smaller) < R(larger). When the resistors are connected in se

ASHA 777 [7]

Answer:

R = 9.85 ohm , r = 0.85 ohm

Explanation:

Let the two resistances by r and R.

when they are connected in series:

V = 12 V

i = 1.12 A

The equivalent resistance when they are connected in series is

Rs = r + R

So, By using Ohm's law

V = i Rs

Rs = V / i = 12 / 1.12 = 10.7 ohm

R + r = 10.7 ohm .... (1)

When they are connected in parallel:

V = 12 V

i = 9.39 A

The equivalent resistance when they are connected in parallel

$R_{p}=\frac{R+r}{rR}$

So, By using Ohm's law

V = i Rp

Rp = V / i = 12 / 9.39 = 1.28 ohm

$\frac{R+r}{rR}=1.28$ .... (2)

by substituting the value of R + r from equation (1) in equation (2), we get

r R = 8.36 ..... (3)

$R-r = \sqrt{\left ( R+r \right )^{2}-4rR}$

$R-r = \sqrt{\left ( 10.7 \right )^{2}-4\times 8.36}=9$ ..... (4)

By solvng equation (1) and (4), we get

R = 9.85 ohm , r = 0.85 ohm

8 0

3 years ago

You skip north for 12 minutes to your best friend's house that is 1.5 kilometers away. What is your average velocity?

bagirrra123 [75]

Answer:

The average velocity is 7.5 km/h

Explanation:

Let's convert minutes to hours so our answer can be given in a common units of km/hour:

12 minutes = 12/60 hours = 0.2 hours

Now we estimate the average velocity calculating the distance travelled over the time it took:

1.5 / 0.2 km/h = 7.5 km/h

3 0

3 years ago

This force is involves the attraction between charged particles

Nikolay [14]

That's the 'electrostatic' force.

6 0

3 years ago

Read 2 more answers