Unit 3 Quiz 1 RETAKE

Match the following

• Joules (J)

• Distance

• Watts (W)

• Power

• Meters (m)

• Work

• Newtons (N)

• Force

Tags

3.1.1

Which has more momentum: a car stopped at a red light or a bike moving at 15 mph?

• car

• bike

• they are equal

Answer explanation

Momentum is the product of mass and velocity. The car at a red light has zero velocity, thus zero momentum. The bike moving at 15 mph has momentum, making it the one with more momentum.

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3.1.1a

A 50 kg ball rolls down the street at 5 m/s. Calculate the momentum of the ball. 

• 55 kg*m/s

• 100 kg*m/s

• 250 kg*m/s

• 500 kg*m/s

Answer explanation

Momentum is calculated using the formula: momentum = mass × velocity. Here, mass = 50 kg and velocity = 5 m/s. Thus, momentum = 50 kg × 5 m/s = 250 kg*m/s, which is the correct answer.

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3.1.1a

Imagine you are a football coach. You want to pick the player who would be hardest to stop when running through the defense.

Based on their masses and velocities, which player has the greatest momentum?

• The player with the lowest mass and highest velocity.

• The player with the highest mass but no velocity.

• The player with the highest mass and highest velocity.

• The player with the highest mass and lowest velocity.

Answer explanation

Momentum is calculated as mass times velocity. The player with the highest mass and highest velocity will have the greatest momentum, making them the hardest to stop when running through the defense.

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3.1.1a

Two ice skaters, standing still on ice, push off each other and move in opposite directions. Skater A is lighter than Skater B.

Which statement best explains what happens according to the Law of Conservation of Momentum?

• Skater B moves away faster than Skater A.

• Both skaters move away at the same speed.

• Skater A does not move at all.

• Skater A moves away faster than Skater B.

Answer explanation

According to the Law of Conservation of Momentum, when two skaters push off each other, the momentum before and after must be equal. Since Skater A is lighter, they will move away faster than Skater B.

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3.1.1b

Two balls roll toward each other and bounce off when they collide. Ball A rolls to the right, and Ball B rolls to the left.

What happens to their momentum after they bounce?

• The total momentum of the system is the same after they bounce.

• The total momentum of the system increases after they bounce.

• The total momentum of the system decreases after they bounce.

Answer explanation

The total momentum of a system is conserved in collisions, meaning it remains the same before and after the bounce. Therefore, the correct choice is that the total momentum of the system is the same after they bounce.

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3.1.1b

Two cars with the same mass are moving in the same direction. Car A is going faster than Car B. They crash and stick together.

What happens to their speed right after they stick together?

• The speed of the combined cars will be equal to Car B's speed.

• The combined cars will move faster than Car A's original speed.

• The speed of the combined cars will be between the speeds of Car A and Car B.

• The combined cars will stop immediately after the crash.

Answer explanation

When two cars of the same mass collide and stick together, their combined speed will be a weighted average of their speeds. Since Car A is faster than Car B, the speed of the combined cars will be between the speeds of Car A and Car B.

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3.1.1b

Which of the following situations shows that work is being done on an object?

• Holding a book without moving it.

• A pencil sitting on a table.

• Watching a car drive by.

• Pushing a box across the floor.

Answer explanation

Work is done on an object when a force causes it to move. Pushing a box across the floor involves applying a force that results in movement, demonstrating that work is being done. The other options do not involve movement.

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3.1.1c

A kid throws a ball with a force of 70N over 1.1 meters. How much work did he do?

• 77 joules

• 70 joules

• 7.7 joules

• 11 joules

Answer explanation

Work is calculated using the formula: Work = Force x Distance. Here, Work = 70N x 1.1m = 77 joules. Therefore, the correct answer is 77 joules.

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3.1.1c

A student pushes a boulder up a hill.

(1) Has work been done? (a)  

(2) How do you know? (b)  

• No.

• There was no movement

• Force was applied, and an object moved

• Yes.

Answer explanation

Yes, work has been done because a force was applied to the boulder, and it moved up the hill. This movement indicates that work, defined as force applied over a distance, has occurred.

Tags

3.1.1c