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Andreyy89
3 years ago
5

Researchers conducted an experiment to identify the effects of three different hand sanitizers on the growth of bacteria. The re

searchers grew one type of bacteria in twenty-four identical covered petri dishes. Then, they opened eighteen petri dishes and applied the three hand sanitizers to six petri dishes each. They left the remaining six petri dishes closed as a control group. When the researchers measured the growth of bacteria two days later, the six dishes that had no hand sanitizer showed the least amount of bacterial growth. The researchers concluded that not using any hand sanitizer would lead to the least bacterial growth.
Which statement best explains why the researchers’ conclusion was not justified?
The experiment tested too many variables.
The control group was not treated the same as the experimental group.
The sample size of twenty-four petri dishes is not large enough.
The single type of bacteria is not adequate to make any conclusions.
Physics
2 answers:
pickupchik [31]3 years ago
7 0
Picture ? I need a visual reference
mafiozo [28]3 years ago
3 0

Answer:

The correct answer will be option-The control group was not treated the same as the experimental group.

Explanation:

A scientific experiment is performed to test the predicted hypothesis which in the given case is that "different hand sanitizes have a different effect on the growth of the bacteria".

The researcher divides 24 samples into two groups- 18 Petri-dishes divided into 3 groups with 6 Petri dish receiving different sanitizers each and rest 6 as control samples without treatment of the hand sanitizers.

The researcher performed the mistake while doing the experiment as he opened the experimental Petri dishes and kept them open whereas in the control group he kept the Petri dish closed which lead to the error in the results as the control showed least growth of the bacteria which should be high.  

This happened because the control and the experimental samples were not provided with the same question and thus is the correct answer.

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When a person plucks a guitar string, the number of half wavelengths that fit into the length of the string determines the _____
Vedmedyk [2.9K]

Answer:

Frequency

Explanation:

Each half wavelength has a point of largest amplitude (aka a node). Depending on the wavelength each node oscillates at a certain rate of swings per unit of time. The latter is referred to as frequency and measure in Hertz [Hz].

8 0
3 years ago
Is fe a reactant or product
DedPeter [7]
Reactant is the answer
4 0
3 years ago
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FIGURE 2 shows a 1.5 kg block is hung by a light string which is wound around a smooth pulley of radius 20 cm. The moment of ine
Sindrei [870]

Answer:

At t = 4.2 s

Angular velocity: 6. 17 rad /s

The number of revolutions: 2.06

Explanation:

First, we consider all the forces acting on the pulley.

There is only one force acting on the pulley, and that is due to the 1.5 kg mass attached to it.

Therefore, the torque on the pulley is

\tau=Fd=mg\cdot R

where m is the mass of the block, g is the acceleration due to gravity, and R is the radius of the pulley.

Now we also know that the torque is related to angular acceleration α by

\tau=I\alpha

therefore, equating this to the above equation gives

mg\cdot R=I\alpha

solving for alpha gives

\alpha=\frac{mgR}{I}

Now putting in m = 1.5 kg, g = 9.8 m/s^2, R = 20 cm = 0.20 m, and I = 2 kg m^2 gives

\alpha=\frac{1.5\cdot9.8\cdot0.20}{2}\boxed{\alpha=1.47s^{-2}}

Now that we have the value of the angular acceleration in hand, we can use the kinematics equations for the rotational motion to find the angular velocity and the number of revolutions at t = 4.2 s.

The first kinematic equation we use is

\theta=\theta_0+\omega_0t+\frac{1}{2}\alpha t^2

since the pulley starts from rest ω0 = 0 and theta = 0; therefore, we have

\theta=\frac{1}{2}\alpha t^2

Therefore, ar t = 4.2 s, the above gives

\theta=\frac{1}{2}(1.47)(4.2)^2

\boxed{\theta=12.97}

So how many revolutions is this?

To find out we just divide by 2 pi:

\#\text{rev}=\frac{\theta}{2\pi}=\frac{12.97}{2\pi}\boxed{\#\text{rev}=2.06}

Or about 2 revolutions.

Now to find the angular velocity at t = 4.2 s, we use another rotational kinematics equation:

\omega^2=w^2_0+2\alpha(\Delta\theta)_{}

Since the pulley starts from rest, ω0 = 0. The change in angle Δθ we calculated above is 12.97. The value of alpha we already know to be 1.47; therefore, the above becomes:

\omega^2=0+2(1.47)(12.97)w^2=38.12\boxed{\omega=6.17.}

Hence, the angular velocity at t = 4.2 w is 6. 17 rad / s

To summerise:

at t = 4.2 s

Angular velocity: 6. 17 rad /s

The number of revolutions: 2.06

3 0
1 year ago
A bullet is fired horizontally at a height of 1.3 meters and a velocity of 950 m/s. How long was the bullet in the air?
seropon [69]

Answer:

<em>The bullet was 0.52 seconds in the air.</em>

Explanation:

<u>Horizontal Motion </u>

It occurs when an object is thrown horizontally with a speed v from a height h.

The object describes a curved path ruled exclusively by gravity until it hits the ground.

To calculate the time the object takes to hit the ground, we use the following equation:

\displaystyle t=\sqrt{\frac{2y}{g}}

Note it doesn't depend on the initial velocity but on the height.

The bullet is fired horizontally at h=1.3 m, thus:

\displaystyle t=\sqrt{\frac{2\cdot 1.3}{9.8}}

\displaystyle t=\sqrt{\frac{2.6}{9.8}}

t = 0.52 s

The bullet was 0.52 seconds in the air.

3 0
3 years ago
Which characterstic is related to kinetic enegry but not potential energy.
V125BC [204]

Answer:

A

Explanation:

Kinetic energy is the energy of motion

KE=.5mv^2

>m= mass

>v= velocity (m/s)

PE=mgh

>m= mass

>g= acceleration due to graviry

>h= height

8 0
2 years ago
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