Unit 8.1 Quiz 8

In the cart-box system, friction causes:

• so much thermal energy that the box catches on fire.

• the cart and box to slow down to a stop.

• the cart and box to stay on the track and not fly away.

• the cart and box to move faster and fall off the track.

Answer explanation

Friction opposes motion, causing the cart and box to lose kinetic energy and slow down until they eventually stop. This is why the correct answer is that friction causes the cart and box to slow down to a stop.

Tags

NGSS.MS-PS2-2

The upward force on an object falling through the air is:

• inertia.

• gravity.

• acceleration.

• air resistance.

Answer explanation

The upward force on an object falling through the air is primarily due to air resistance, which opposes the downward force of gravity. This force increases with speed and surface area, affecting the object's fall.

A cart with a sail travels slower than a cart without a sail, especially when traveling into a headwind because:

• gravity is pulling down harder on the cart with the sail.

• friction is greater on the cart with the sail.

• the cart with the sail has more inertia.

• the cart with the sail experiences more air resistance.

Answer explanation

The cart with the sail experiences more air resistance, especially when facing a headwind. This increased drag slows it down compared to a cart without a sail, which has less surface area exposed to the wind.

Rougher surfaces (compared to smoother surfaces) have:

• less friction.

• greater friction.

• the same friction.

• no friction.

Answer explanation

Rougher surfaces have greater friction because the irregularities in their texture create more resistance against sliding. This increased contact area leads to higher friction compared to smoother surfaces.

The graph shows how pitch speed is related to wind speed. Pitch speed is on the Y-axis (vertical) and wind speed is on the x-axis (horizontal). Points A, B, and C represent three of the same type of fast pitch all thrown at the same initial speed from the pitcher’s fingertips, but under different wind conditions. What is true about the amount of kinetic energy each pitch would have when it reaches home plate?

• Pitch A would have the least kinetic energy.

• Pitch B would have the least kinetic energy.

• Pitch C would have the least kinetic energy.

• They would all have the same kinetic energy.

Answer explanation

Pitch C would have the least kinetic energy because it is affected by higher wind speed, which reduces its speed as it travels to home plate, resulting in lower kinetic energy compared to pitches A and B.

Tags

NGSS.MS-PS3-1

NGSS.MS-PS3-5

The data table shows how fast a major league power hitter can swing a bat with different amounts of mass. The data from the table has been plotted on the graph shown. If a batter can apply the same amount of maximum force from their hands to each bat to swing it, why would the speed of the bat swing decrease as the mass of the bat increases?

• Energy is not required to change the speed of an object, but force is.

• If the force is the same and the mass is greater, the change in speed must be greater.

• If the force is the same and the mass is greater, the change in speed must be less.

• If the force is the same, it takes the same amount of energy to move an object no matter how heavy it is.

Answer explanation

If the force applied is constant and the mass of the bat increases, the acceleration (and thus the change in speed) must decrease according to Newton's second law (F=ma). Therefore, the speed of the bat swing decreases.

Tags

NGSS.MS-PS2-2

NGSS.MS-PS3-1

Use the data tables and any investigation results you remember to answer the following:

Which has a bigger effect on the speed of a ball after the bat and ball make contact, the mass of the bat or the bat swing speed?

• The bat swing speed has a bigger effect on the speed of the ball.

• The mass of the bat has a bigger effect on the speed of the ball.

• The mass of the bat and the bat swing speed have the same effect on the speed of the ball.

Answer explanation

The bat swing speed significantly influences the ball's speed upon contact, as a faster swing transfers more kinetic energy to the ball compared to the bat's mass. Therefore, the bat swing speed has a bigger effect on the speed of the ball.

Tags

NGSS.MS-PS2-1

NGSS.MS-PS2-2

In a previous question, you were asked, "Which has a bigger effect on the speed of a ball after the bat and ball make contact, the mass of the bat or the bat swing speed?"

Explain your response to that question.

• In our investigations the faster cart moved the box farther. The data tables show more change to the speed of the ball when the bat swing speed is increased.

• In our investigations, when we changed mass and speed of the cart, the results were the same. According to the data tables there isn't much difference between changing mass or speed.

• In our investigations the cart with more mass moved the box further. Also, the data tables show more change to the speed of the ball when the mass of the bat is increased.

Answer explanation

The investigation showed that increasing the bat swing speed had a greater impact on the ball's speed than changing the mass of the bat. The data indicates that faster swings result in more significant changes in the ball's speed.

Tags

NGSS.MS-PS2-1

NGSS.MS-PS2-2