Ascientist wants to perform a controlled experiment to test the effect of rust on chemically treated iron. which action would be most important to perform in a controlled experiment? design an experiment that is based on previously published results. expose the treated iron to the corrosive effects of the air. test a large piece of treated iron and a small piece of untreated iron. test a piece of treated iron and a piece of untreated iron under the same conditions.

Test a piece of treated iron and a piece of untreated iron under the same conditions.

Explanation:

A controlled experiment is the one where a control variable is used. A control variable is the one which does experience any test in the experiment. Instead it is kept as a standard benchmark for comparison with the variables used in the experiment.

According to the given situation, Test a piece of treated iron and a piece of untreated iron under the same conditions. is the correct option because in this a tested sample that is treated with a chemical agent is used along with a piece of untreated iron under the same conditions. This will give indication of the affect of treatment on the iron under conditions which can cause rust.

weight of the box is given as

here this is placed on the inclined of angle 42 degree

now this weight will have two components one is along the incline other is perpendicular to it

so here we need to apply a force parallel to incline opposite to its component of weight

so here the component of weight is given as

here we have

so it requires 75 n force to move it upwards

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.