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lilavasa [31]
3 years ago
10

A person is standing on a scale placed on the floor of an elevator. At time t, the elevator is at rest and the reading on the sc

ale is 500 N. At a later time ty, the person is still standing
on the scale and the reading on the scale is 400 N. Based on the scale readings, which of the following statements about the motion of the elevator could be true at time to?
A.
The elevator is moving upward at constant speed
B.
The elevator is moving upward and slowing down.
C.
The elevator is moving downward at constant speed.
D.
The elevator is moving downward and slowing down,
E.
The elevator is at rest.​
Physics
1 answer:
larisa [96]3 years ago
8 0

Answer:

A- The elevator is moving upward at constant speed

Explanation:

am not sure of my answer but I think this is the most logical answer

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A tortoise and hare start from rest and have a race. As the race begins, both accelerate forward. The hare accelerates uniformly
Mnenie [13.5K]

Answer:

The acceleration of the hare once it begins to slow down is -0.68 m/s²

The acceleration of the tortoise is 0.28 m/s²

Explanation:

The equations that describe the position and velocity of the hare and the tortoise are the following:

x = x0 + v0 · t + 1/2 · a · t²

v = v0 + a · t

Where:

x = position at time t

x0 = initial position

v0 = initial velocity

t = time

a = acceleration

v = velocity at time t

To find the acceleration of the hare once it begins to slow down, we have to find how much time the hare traveled during the deceleration and what was its initial speed.

First, the hare moves with constant acceleration for 4.7 s. Then, its velocity at  t = 4.7 s will be:

v = v0 + a · t    (v0 = 0 because the hare starts form rest)

v = a · t = 0.9 m/s² · 4.7 s = <u>4.2 m/s</u>

<u />

The distance traveled by the hare while accelerating can be calculated using the equation of the position:

x = x0 + v0 · t + 1/2 · a · t²      (x0 = 0 and v0 = 0)

x = 1/2 · a · t² = 1/2 · 0.9 m/s² · (4.7)² = <u>9.9 m</u>

<u />

Then, the hare runs at a constant speed of 4.2 m/s for 11.7 s. The distance traveled at constant speed will be:

x =  v · t

x = 4.2 m/s · 11.7 s = <u>49.1 m</u>

<u />

Then, the distance traveled by the hare while slowing down was:

Distance traveled while slowing down = 72 m - 49.1 m - 9.9 m = 13 m

Let´s find how much time it took the hare to come to stop, so we can calculate the acceleration. We know that when the position is 13 m, the velocity is 0.

v = v0 + a · t

0 = 4.2 m/s + a · t

-4.2 m/s / t = a

Replacing in the equation of the position:

x = v0 · t + 1/2 · a · t²      (considering x0 as the point at which the hare started to slow down)

13 m = 4.2 m/s · t - 1/2 · 4.2 m/s / t · t²

13 m = 4.2 m/s · t - 2.1 m/s · t

13 m = 2.1 m/s · t

t = 13 m / 2.1 m/s

t = 6.2 s

Then, the acceleration of the hare while slowing down will be:

-v0/t = a

-4.2 m/s / 6.2 s = a

a = -0.68 m/s²

The acceleration of the hare once it begins to slow down is -0.68 m/s²

The hare traveled 72 m in (6.2 s + 11.7 s + 4.7 s) 22.6 s. The tortoise reaches the final position of the hare at the same time, so, using the equation of the position we can calculate the acceleration of the tortoise:

x = x0 + v0 · t + 1/2 · a · t²     (x0 = 0 and v0 = 0)

x = 1/2 · a · t²

72 m = 1/2 · a · (22.6 s)²

144 m / (22.6 s)² = a

a = 0.28 m/s²

The acceleration of the tortoise is 0.28 m/s²

6 0
3 years ago
An alpha particle has a charge of +2e and a mass of 6.64 x 10-27 kg. It is accelerated from rest through a potential difference
kondor19780726 [428]

Answer:

a) v = 1.075*10^7 m/s

b) FB = 7.57*10^-12 N

c) r = 10.1 cm

Explanation:

(a) To find the speed of the alpha particle you use the following formula for the kinetic energy:

K=qV          (1)

q: charge of the particle = 2e = 2(1.6*10^-19 C) = 3.2*10^-19 C

V: potential difference = 1.2*10^6 V

You replace the values of the parameters in the equation (1):

K=(3.2*10^{-19}C)(1.2*10^6V)=3.84*10^{-13}J

The kinetic energy of the particle is also:

K=\frac{1}{2}mv^2       (2)

m: mass of the particle = 6.64*10^⁻27 kg

You solve the last equation for v:

v=\sqrt{\frac{2K}{m}}=\sqrt{\frac{2(3.84*10^{-13}J)}{6.64*10^{-27}kg}}\\\\v=1.075*10^7\frac{m}{s}

the sped of the alpha particle is 1.075*10^6 m/s

b) The magnetic force on the particle is given by:

|F_B|=qvBsin(\theta)

B: magnitude of the magnetic field = 2.2 T

The direction of the motion of the particle is perpendicular to the direction of the magnetic field. Then sinθ = 1

|F_B|=(3.2*10^{-19}C)(1.075*10^6m/s)(2.2T)=7.57*10^{-12}N

the force exerted by the magnetic field on the particle is 7.57*10^-12 N

c) The particle describes a circumference with a radius given by:

r=\frac{mv}{qB}=\frac{(6.64*10^{-27}kg)(1.075*10^7m/s)}{(3.2*10^{-19}C)(2.2T)}\\\\r=0.101m=10.1cm

the radius of the trajectory of the electron is 10.1 cm

6 0
4 years ago
¿Qué diferencia una magnitud fundamental de una derivada?
artcher [175]

Answer:

Explanation:

Una magnitud fundamental es aquella que se define por si misma y es independiente de las demás (masa, tiempo, longitud, etc.). magnitud derivada. Una magnitud derivada es aquella que se obtiene mediante expresiones matemáticas a partir de las magnitudes fundamentales (densidad, superficie, velocidad).

7 0
3 years ago
Read 2 more answers
In an experiment, a ringing bell is placed in a vacuum jar that does not have any air in it. What best describes why the bell is
madam [21]

Answer:

Light does not need a medium to travel travel through, but since waves must have a medium to vibrate, sound is not created where no air is present.

Explanation:

3 0
3 years ago
Why do disk stars bob up and down as they orbit the galaxy?
Pie

Answer:

When the stars get a little bit farther from the disk, the other stars that are still in the disk will pull them toward it as a consequence of the gravity between them.

     

Explanation:

Galaxies have different structures due to parameters as the orbit of the stars around the center of the galaxy or the metallicity¹ of the stars (which serves to find the age of the stars). For example, in the case of the Milky Way, it has:

       

The Halo

The Bulge

The Thick Disk

The Thin Disk

The Halo has old stars with low metallicities and random orbits, while the bulge has stars with the same random motions like the one in the Halo.

The Thick Disk has stars with orbits oriented in the same direction but with  metallicities a little bit higher than the one from the Halo but lower than the stars in the Thin Disk.

The stars that are in the thin disk have orbits oriented in the same direction and are the ones with the higher metallicity levels, which means that they are the most younger in the galaxy.

In general the stars in the disk of the galaxy (thick disk and thin disk) goes up and down as they orbit the center of the galaxy, <u>the reason for this is that when they get a little bit farther from the disk, the stars that are still in the disk pull them back toward it as a consequence of the gravity between them. </u>

Remember the equation of the Universal gravitation law:

F = G\frac{m1.m2}{R^{2}}  (1)

Where F is the force of gravity, G is the gravitational constant, m1 and m2 are the masses of two objects and R is the distance between them.

       

Notice how equation 1 expresses that the force of gravity is inversely proportional to the square of the distance between the two objects, which means that the force of gravity will decrease as the square of the distance increase.

                   

Key terms:

¹Metallicity: the abundance of heavier elements against the presence of Helium or Hydrogen.

7 0
3 years ago
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