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1 year ago

For elevator questions, does the weight of a person increase when the elevator is going up or if it's going down-

Physics

1 answer:

TiliK225 [7]1 year ago

6 0

The weight of a person increase when the elevator is going up.

<h3>Weight of the person in the elevator</h3>

The weight of the person in the elevator is calculated as follows;

<h3>When the person is going up</h3>

F = ma + mg

F = m(a + g)

where;

a is acceleration of the person
g is acceleration due to gravity

<h3>When the person is going down</h3>

F = mg - ma

F = m(g - a)

Thus, the weight of a person increase when the elevator is going up.

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Krista is playing tennis at the park. When the tennis ball flies toward her, Krista hits the ball with her racket, which causes

xenn [34]

Answer:

B. When the racket hits the tennis ball with a force, the tennis ball applies an equal but opposite force to the racket.

Explanation:

According to the Newton's third law of motion every action has equal and opposite reaction. So, when the force is applied by the racket on the ball then the ball also applies an equal intensity of force in the opposite direction on the racket. It is just that the the force on the racket is absorbed by the player holding it.

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3 years ago

You wish to cook some pasta and so take some water and heat it on a stove. If you use 2000 grams of water with an initial temper

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Answer:

the stove energy went into heating water is 837.2 kJ.

Explanation:

given,

mass of water = 2000 grams

initial temperature = 0° C

Final temperature = 100° C

specific heat of water (c) = 4.186 joule/gram

energy = m c Δ T

= 2000 × 4.186 × (100° - 0°)

= 837200 J

= 837.2 kJ

hence, the stove energy went into heating water is 837.2 kJ.

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2 years ago

What is the strength of the electric field in a region where the electric potential is constant?

Roman55 [17]

Answer:

Where the electric potential is constant, the strength of the electric field is zero.

Explanation:

As a test charge moves in a given direction, the rate of change of the electric potential of the charge gives the potential gradient whose negative value is the same as the value of the electric field. In other words, the negative of the slope or gradient of electric potential (V) in a direction, say x, gives the electric field (Eₓ) in that direction. i.e

Eₓ = - dV / dx ----------(i)

From equation (i) above, if electric potential (V) is constant, then the differential (which is the electric field) gives zero.

<em>Therefore, a constant electric potential means that electric field is zero.</em>

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3 years ago

Ety ratio

horrorfan [7]

3) The work done is D. zero

4) The kinetic energy is B. 180 J

5) The potential energy is A. 120 J

6) The work done depends on B. position

7) The example of non-renewable energy is C. coal

8) The power expended is $3\cdot 10^4 W$

9) The efficiency is A. 100%

10) The velocity ratio is 5

Explanation:

The work done by a force acting an object is given by:

$W=Fd cos \theta$

where :

F is the magnitude of the force

d is the displacement

$\theta$ is the angle between the direction of the force and the displacement

When the force is applied perpendicular to the direction of motion,

$\theta=90^{\circ}$

Therefore, the work done is:

$W=Fd(cos 90^{\circ})=0$

The kinetic energy of a body is given by

$K=\frac{1}{2}mv^2$

where

m is the mass of the body

v is its speed

For the girl in this problem, we have

m = 40 kg

v = 3 m/s

Therefore her kinetic energy is

$K=\frac{1}{2}(40)(3)^2=180 J$

The potential energy of an object is given by

$PE=mgh$

where

m is the mass

$g=10 m/s^2$ is the acceleration of gravity

h is the heigth of the object relative to the ground

For the ball in this problem,

m = 0.4 kg

h = 30 m

So, the potential energy is

$PE=(0.4)(10)(30)=120 J$

A conservative field is a field for which the work done by the field on an object does not depend on the path taken, but only on the initial and final position of the object.

Gravitational and electric fields are examples of conservative fields. In fact:

When an object is pulled down by gravity (free fall), the work done by the gravitational field only depends on the change in height $\Delta h$ between the two points, not on the path taken during the fall
When an electric charge is pushed by the electric field, the work done by the field depends only on the initial and final position of the charge in the field

For any conservative field, it is possible to define a "potential" function, which represents the energy per unit mass/charge, and depends only on the position of the object.

Non-renewable energy sources are sources of energy whose rate of consumption is faster than the rate at which they are re-created. Examples of non-renewable sources are coal, oil, natural gas. These energy sources are consumed at a fast rate, while they take million of years to regenerate, so at the current rate they will eventually run out.
Renewable energy sources are sources of energy that replenish at faster rate than the rate at which it is consumed. Examples of renewable sources are solar energy, wind, hydroelectric power.

Therefore, the example of non-renewable energy in this case is

C. Coal

For an object pushed by a force F and moving at a constant velocity v, the power expended is given by

$P=Fv$

where F is the force and v is the velocity.

for the rocket in this problem, we have:

F = 10 N is the force propelling the rocket

v = 3000 m/s is its velocity

Substituting into the equation, we find the power expended:

$P=(10)(3000)=30,000 W = 3\cdot 10^4 W$

The efficiency of a machine is given by

$\eta = \frac{W_{out}}{W_{in}}$

where

$W_{in}$ is the energy in input to the machine

$W_{out}$ is the useful work in output from the machine

For a real machine, the useful work in output is always lower than the energy input, because part of the energy is "wasted" and converted into thermal energy due to the presence of internal frictions. However, for an ideal machine, all the input energy is converted into useful work, so

$W_{out}=W_{in}$

And therefore the efficiency is

$\eta=1$

which means 100%.

10.

The velocity ratio of a block and tackle system is the ratio between the distance moved by the effort and the distance moved by the load.

$VR=\frac{d_{eff}}{d_{load}}$

In a block and tackle system, the velocity ratio is also equal to the number of pulleys in the system.

For the system in the problem, there are 5 pulleys: therefore, this means that when the effort moves 5 metres, the load moves 1 metres, therefore the velocity ratio is

$VR=\frac{5}{1}=5$

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3 years ago

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Answer:

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