Newton's Laws of Motion - End of Week Assessment

When forces applied to an object from both sides, but the object stays at rest (does not move), this would be an example of what kind of forces?

• Unbalanced forces

• Balanced forces

Answer explanation

Balanced forces are those that are opposite in direction and equal in size. Balanced forces are considered to be in a state of equilibrium. When forces are balanced there is no change in direction. Combined forces that are balanced are always equal to zero.

Which of the following is an example of an unbalanced force?

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Answer explanation

To have unbalanced forces means that the force applied in one direction is greater than the force applied in the opposite direction. When unbalanced forces are acting on an object, there is a change in speed and/or direction.

Tags

NGSS.MS-PS2-1

NGSS.MS-PS2-2

How will this object move? 

• It won't move. 

• It will move to the right. 

• It will move to the left. 

• It will move upwards. 

• It will move downwards.

Answer explanation

The forces in this picture are unbalanced.

We see a force of 50 N pushing the object to the right, and a force of 30 N pushing the object to the left. Since the force pushing to the right is greater, it will overcome the other force, and the object will move to the right with a remaining force of 20 N

Tags

NGSS.MS-PS2-1

NGSS.MS-PS2-2

You and your friend are moving a couch from one side of the room to another. Your buddy pushes with a force of 35 N to the right and you push with a force of 25 N right. What is the net force on the couch?

• 60 N to the right

• 10 N to the left

• 10 N to the right

• 50 N to the left

• 50 N to the right

Answer explanation

In this case, both forces are acting on the same side of the object and pushing in the same direction. Therefore, we will add the forces together in order to calculate the net force.

Tags

NGSS.MS-PS2-2

Calculate the net forces acting on the object.

• 40 N, Left

• 40 N, Right

• 0 N, Balanced

• 75 N, Right

Answer explanation

We see several forces acting on this object.

The most efficient way to go about solving this is to add up all the forces acting to the right, then all t he forces acting to the left, and subtract on another to find the net force.

In the diagram, we see two separate forces acting to the left: 20 N and 35 N for a total of 55 N.

We see only one single force of 55 N acting on the right. Since the left and right forces are both 55 N, they would cancel each other out and we would have a net force of 0 N - BALANCED

Tags

NGSS.MS-PS2-2

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Answer explanation

This is a little trickier as it involves reading data from a graph, but the concepts are the same.

Speed is the change in distance, divided by the change in time. We can calculate this using the data on the graph.

From 0-3 seconds, the car goes from 0 to 4.5 meters. The change in distance is 4.5 m and the change in time is 3 s, so 4.5/3 = 1.5 m/s

From 3-6 seconds, the car's distance does not change. It starts and ends at 4.5 meters. Therefore, since the change in distance is 0, the speed is 0 as well.

Finally, from 6-9 seconds, the car goes from 4.5 meters to 7.5 meters. This means the change in distance was 3 meters, over a time of 3 seconds. 3 divided by 3 is 1, and therefore the speed of the car from 6-9 seconds is 1 m/s

Tags

NGSS.MS-PS3-1

Looking at the chart, which of the following descriptions most accurately describes what is being depicted.

• Carleton walked for a while, stopped to sit on a bench in the park, and then ran the rest of the way home.

• Carleton ran all the way from school to home going the same constant speed and never stopping.

• Carleton waited around after school for his friend, and then they ran home together.

• Carleton ran for a long time, then slowed down to walk the rest of his trip. Once he got home, he sat down on the couch.

Answer explanation

In this case, we see a chart of a line pointing upwards, without any variations. The slope of the line is consistent, and therefore, we know the speed is consistent (constant).

If there was a slow down or speed up at any point, we would see variations in the line. The line would either dip downwards and shoot upwards more steeply. We do not see this at all.

If at any point the speed was zero in the chart, we would see the line flatten out horizontally, but we do not see this either.

The line is consistent and pointing upwards and therefore, the speed was constant.

Tags

NGSS.MS-PS3-1

Which of the following descriptions most accurately describes what is being depicted in the chart?

• Jessica ran all the way from school to home going the same constant speed and never stopping.

• Jessica waited around after school for her friend, and then they ran home together.

• Jessica ran for a long time, then slowed down to walk the rest of her trip. Once she got home, she sat down on the couch.

• Jessica walked for a while, stopped to sit on a bench in the park, and then ran the rest of the way home.

Answer explanation

In this chart, we see a line with multiple variations, so that should tell us different things are happening.

The first segment of the line is pointing upwards, so we know the speed is not zero, but the line is also not very steep, which means the object is not moving too quickly.

Then, we see the line level out horizontally. This tells us the speed is currently zero.

Finally, we see the line become very steep, pointing upwards, which indicates the object is moving quickly.

If we look to the answer choices, we see one which matches our data.

Jessica started out walking (slower speed), then stopped and sat on a bench (speed is zero), and then she ran (fast speed) all the way home.

We did it!

Tags

NGSS.MS-PS3-1

After how much time did the train make its first stop?

• 0 hours

• 4 hours

• 6 hours

• 12 hours

Answer explanation

We know that since this chart shows distance over time, it is a chart depicting speed.

When the line of the chart is flat (horizontal), we know this indicates a stop, or a speed of zero.

In this chart, we see the first horizontal line at 4 hours, which indicates the first stop of the train.

Tags

NGSS.MS-PS3-1

What is the motorcycle's average speed, in kilometers per minute, over the first four minutes?

(Average speed = total distance / total time)

• 6.25 km/min

• 21 m/s

• 0.16 km/min

• 100 m/s

Answer explanation

All we need to do here is divide the total distance traveled in 4 minutes (25 kilometers), by the time, which is 4 minutes.

25/4 = 6.25 km/min

Tags

NGSS.MS-PS3-1