Unit 2 Test Corrections

16. The chemical formula for carbonic acid is H₂CO₃. Which statement describes the number of atoms in THREE molecules of carbonic acid?

• Three molecules of carbonic acid would contain 2 atoms of hydrogen, 1 atom of carbon, and 3 atoms of oxygen.

• Three molecules of carbonic acid would contains 2 atoms of hydrogen, 3 atoms of carbon and 1 atom of oxygen.

• Three molecules of carbonic acid would contain 6 atoms of hydrogen, 3 atoms of carbon, and 9 atoms of oxygen.

• Three molecules of carbonic acid would contain 6 atoms of hydrogen, 9 atoms of carbon, and 9 atoms of oxygen.

Answer explanation

The formula H₂CO₃ is shown. The subscript belongs ONLY to the element in front of it therefore, there are 2 hydrogen atoms, 1 carbon atom, and 3 oxygen atoms. BUT ....the question asks for the number of atoms in THREE molecules of the substance. That changes the chemical formula to 3H₂CO₃. Now you must multiply all the atoms by three. This will make the totals 6 hydrogen (2x3), 3 carbon (1x3), and 9 oxygen (3x3).

Tags

NGSS.MS-PS1-1

Two horses pull in opposite directions but together move in the direction shown. Horse 1 pulls with a force of 1560 N. If the net force is 117 N, which of the following measurements must be the force applied by Horse 2? 

• 1443 N

• 1677 N

• 1562 N

• 1560 N

Answer explanation

The direction of the force is to the right. That means that the highest number should be on the right. The problem tells us that the darker horse (2) is moving to the right with 177 N of force. That means that the number for horse 2 should be the force for horse 1 + 117N.

Tags

NGSS.MS-PS2-1

NGSS.MS-PS2-2

Carts of different masses are pulled along a flat surface. The table shows some variables for each cart.

Which two carts experience the same net force?

• A. Carts 1 and 2

• B. Carts 1 and 3

• C. Carts 2 and 3

• D. Carts 2 and 4

Answer explanation

The question asks for the net force on the four carts. A force is being applied in one direction and the force of friction is working against it. Since the two forces are working against each other, they should be subtracted to find the net force. Calculate the net force for all four carts in order to find your answer. The mass is not needed and can be ignored.

Tags

NGSS.MS-PS2-2

A student is pushing two blocks on a smooth, frictionless surface with 75N.

What is the acceleration of the blocks? Enter your answer in the box

Answer explanation

The question asked you to find the acceleration of this set of objects. You will need the formula a = f/m. You will need to determine the total mass by adding 10 + 20. You will then use that number for mass and use 75 N for force.

Tags

NGSS.MS-PS2-2

A car is traveling down the street until it comes to a sudden stop at a red light. When the car comes to a sudden stop, two events occur. Event 1: There is no unbalanced force acting on the person driving, so the person initially keeps moving forward. Event 2: The person's forward movement is then stopped by the seat belt exerting a force on the person. The person exerts a force back on the seat belt. Which statement BEST describes the Newton's Laws of Motion acting within each of the 2 events?

• A. Event 1: Newton's First Law of Motion

  Event 2: Newton's Third Law of Motion

• B. Event 1: Newton's Third Law of Motion

  Event 2: Newton's Second Law of Motion

• C. Event 1: Newton's Third Law of Motion

  Event 2: Newton's First Law of Motion

• D. Event 1: Newton's First Law of Motion

  Event 2: Newton's Second Law of Motion

Answer explanation

Newton's 1st Law tells us that an object stays in motion until it's acted on by a force. The car and the rider were in motion. The force of the car's brakes made the car stop but the rider continued to move forward. Newton's 3rd Law says that for every action, there is an equal and opposite reaction. The rider is still moving forward and hits the seatbelt. The seatbelt pushes back with the same amount of force in the opposite direction.

An equation for a chemical reaction is shown below. 

 

CH₄ + 2O₂ ⇒ CO₂ + 2H₂O

 

Which statements below are true about the chemical reaction? 

Choose TWO correct answers. 

• There are 4 hydrogen atoms in the reactants and 2 hydrogen atoms in the products.

• There are 4 oxygen atoms in the reactants and 4 oxygen atoms in the products. 

• The number of atoms of each element in the reactants is equal to the number of atoms of each element in the products. 

• There are more carbon atoms in the reactants than the products. 

• No new substances were produced during the chemical reaction. 

Answer explanation

Look at the red chemical equation. You can see that REACTANTS are on the left and PRODUCTS are on the right.

The subscript belongs ONLY to the element directly in from of it. Therefore, in CH₄, there are 1 carbon and 4 hydrogen atoms. The coefficient in front of 2O₂ must be multiplied by the subscript (2 x 2) so there are 4 oxygen atoms on the reactant side.

On the product side, CO₂ has 1 carbon and 2 oxygen atoms. To determine the atoms in water, you must multiply the coefficient of 2 by everything in the molecule. That means there are 4 hydrogen and 2 oxygen atoms. Use this information to SELECT TWO ANSWERS.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

Which of the following statements is true about the net force on the object in the diagram?

• The vertical net force is 0 N; the horizontal net force is 65 N to the right. 

• The vertical net force is 0 N; the horizontal net force is 65 N to the left. 

• The vertical net force is 65 N to the left; the horizontal net force is 0 N. 

• The vertical net force is 65 N to the right; the horizontal net force is 0 N. 

Answer explanation

You must determine the vertical and horizontal net forces in this diagram. "Vertical" means up and down and is circled in red. "Horizontal" means side to side and is circled in blue. When forces are in opposite directions, they should be subtracted.

The verticle forces shown are 34N and 34N therefore, the net force in that direction is 0. The horizontal forces shown are 12N to the left and 77N to the right. Subtract those numbers and the net force will travel in the direction of the larger force.

Tags

NGSS.MS-PS2-2

A student applied a force of 5 N to a ball with a mass of 12 kg and measured how far the ball rolled. The student wants to complete a second investigation, but he wants the ball to roll a shorter distance than the first investigation. Which actions would achieve the desired results? Choose TWO correct answers.

• A. Roll a ball of the same mass as in the first investigation down a ramp with a force of 5 N.

• B. Apply a 1 N force to a ball of the same mass as the first investigation.

• C. Apply the same amount of force as in the first investigation to a 1 kg ball.

• D. Apply a 20 N force to a ball of the same mass in the first investigation.

• E. Use a 20 kg ball and apply the same amount of force as in the first investigation.

Answer explanation

The ball weighs 12 kg and it is pushed with 5N of force but the ball traveled too hard. Since f=ma, you need to either use less force to push the ball or a ball with more mass. You were supposed to select two answers for this question. Draw the picture in your notes.

Tags

NGSS.MS-PS2-2

8. Four students designed and built air propelled rockets that were launched into the air. Their data are recorded in the table. Which rocket had the greatest acceleration?

• A. Rocket 1

• B. Rocket 2

• C. Rocket 3

• D. Rocket 4

Answer explanation

In order to find the answer, you must know the acceleration of all four rockets. The formula is a=f/m. Look closely at the chart. The mass is one the left and the number goes in the bottom of the formula. Once you have all four numbers for acceleration, decide which one is greatest.

Tags

NGSS.MS-PS2-2

A plastic tube is arranged on a lab tabletop as shown. A small sphere enters one end of the tube with enough speed to come out the other end of the tube. Which diagram shows where the sphere will go first when it leaves the tube?

• 
• 
• 
• 

Answer explanation

Newton's 1st Law states that an object in motion will stay in motion, in the same direction, unless acted on by an unbalanced force. Assume that the sphere is not traveling very fast. When it comes out of the tube it will bounce off the sides if it's going fast but the question asks where it will go FIRST when it exits the tube. The sphere will come out and continue to go in the same direction until acted on by a force. Don't worry about what happens if it bounces off the tube.

Tags

NGSS.MS-PS2-1

NGSS.MS-PS2-2