A student places a drop of purple food into one beaker of water at 20˚C and another drop into another beaker of water at 50˚C. The temperature of the food coloring 19˚C.

Question

What explains what the student observes in this investigation? Select all that apply
A. The food coloring moves faster in hot water.
• B. The food coloring moves slower in hot water.
• C. The food coloring is denser than the cold water.
• D. The food coloring is less dense than the cold water.
• E. The food coloring separates into two different colors.
• F. The food coloring increases the temperature of the water.

Answer 1

In this investigation, the student is observing the behavior of food coloring in water at different temperatures. Here’s an analysis of the options provided:

A. The food coloring moves faster in hot water. - True. Higher temperatures increase the kinetic energy of the molecules, which results in faster diffusion of the food coloring in hot water compared to cold water.

B. The food coloring moves slower in hot water. - False. As mentioned above, food coloring moves faster in hot water due to increased molecular movement.

C. The food coloring is denser than the cold water. - This statement is not relevant to the observed behavior based on temperature. The density of the food coloring compared to water does not directly explain the movement or diffusion in this scenario.

D. The food coloring is less dense than the cold water. - Typically, food coloring is not less dense than water; therefore, this is not a suitable explanation in this context regarding its movement.

E. The food coloring separates into two different colors. - False. Food coloring typically does not separate into different colors upon diffusion in water unless it is specifically designed to do so (like with some types of color-changing or layering colorants).

F. The food coloring increases the temperature of the water. - False. Food coloring itself does not increase the temperature of water; it may alter the color of the water but does not add heat.

Based on these analyses, the correct selection is:

• A. The food coloring moves faster in hot water.

Answer 2

A ball rolls down a grassy hill and eventually comes to a stop. Select three of the reasons the ball comes to a stop.
• A. Friction and drag oppose the motion of the ball.
B. There is no force acting to move the ball forward.
_ C. The force of friction against the ball is decreased.
D. The forces opposing the ball are unbalanced.
E. The force of gravity has increased and stopped the ball.
F. There was too much inertia to keep the ball rolling.

Answer 3

To explain why the ball comes to a stop after rolling down a grassy hill, the following three reasons are relevant:

1. A. Friction and drag oppose the motion of the ball. - True. Friction between the ball and the grass, as well as air drag, act against the motion of the ball, causing it to decelerate and eventually stop.

2. B. There is no force acting to move the ball forward. - True. Once the ball rolls to the bottom of the hill, there is no longer a net force acting in the direction of the motion, leading to its eventual stop.

3. D. The forces opposing the ball are unbalanced. - True. As the ball rolls, the forces acting against it (friction and drag) become greater than the forces propelling it forward (initial push from the slope), which results in an unbalanced force and causes it to stop.

The other options are not applicable for the following reasons:

• C. The force of friction against the ball is decreased. - This is false; the force of friction does not decrease; it acts to stop the ball.

• E. The force of gravity has increased and stopped the ball. - This is misleading; while gravity does act on the ball, it is not the increasing force of gravity that stops it; rather, the friction and drag do.

• F. There was too much inertia to keep the ball rolling. - This is not correct. Inertia keeps an object in motion, but in this case, the opposing forces are what ultimately stop the ball.

So the selected answers are A, B, and D.

Answer 4

A student built a simple electromagnet with copper wire, an iron bolt, and a 1.5-volt battery. The electromagnet was able to life a paper clip from 3 cm away. Select three ways the student can increase the strength of his electromagnet.
• A. He can use a thicker piece of copper wire.
B. He can reverse the orientation of the battery.
C. He can replace the iron bolt with a wooden rod.
• D. He can add a switch between the battery and the iron bolt.
• E. He can replace the 1.5-volt battery with a battery of higher voltage.
F. He can use a longer piece of wire that wraps more times around the bolt.

Answer 5

To increase the strength of the electromagnet, the student can consider the following three options:

1. A. He can use a thicker piece of copper wire. - True. A thicker wire has a lower resistance, which allows more current to flow through the wire, generating a stronger magnetic field.

2. E. He can replace the 1.5-volt battery with a battery of higher voltage. - True. Increasing the voltage of the battery will increase the current flowing through the wire (assuming resistance remains constant), which will enhance the strength of the electromagnet.

3. F. He can use a longer piece of wire that wraps more times around the bolt. - True. Increasing the number of turns of wire around the iron bolt increases the magnetic field strength because the magnetic field strength is proportional to the number of turns of wire.

The other options are less effective in strengthening the electromagnet for the following reasons:

• B. He can reverse the orientation of the battery. - While this will change the direction of the magnetic field, it does not increase the strength of the electromagnet.

• C. He can replace the iron bolt with a wooden rod. - This option would actually weaken the electromagnet since wood is not magnetic and would not contribute to the magnetic field.

• D. He can add a switch between the battery and the iron bolt. - This would not increase the strength; it would only allow control over when the electromagnet is active.

In conclusion, the correct selections are A, E, and F.