Forces Test 3

Emma pushes a shopping cart, and the cart pushes back on her with an equal but opposite force. Which of the laws of motion does this scenario illustrate?

• Newton’s 1st Law

• Newton’s 2nd Law

• Newton’s 3rd Law

• Law of Conservation of Momentum

Answer explanation

Newton’s 3rd Law states, "To every action there is an equal but opposite reaction." This law explains how forces always occur in pairs, making it the correct choice for the given question.

Mia is riding her bicycle down a hill. Which of the following factors does not affect the air resistance she experiences?

• Speed

• Spin

• Size

• Shape

Answer explanation

Air resistance is influenced by speed, size, and shape of an object. Spin does not directly affect air resistance; it may influence the trajectory but not the resistance itself. Therefore, spin is the correct answer.

Aria is pushing a shopping cart at the grocery store. Momentum describes

• How much force is needed to change an object’s motion

• How much velocity changes in a given amount of time

• The tendency of an object to resist a change in motion

• The balanced forces on a falling object with a constant speed

Answer explanation

Momentum is related to how much force is needed to change an object's motion, as it quantifies the motion of an object and its resistance to changes in that motion.

Mia and her friends are comparing different objects to see which has the most inertia. Which of the following items has the most inertia?

• A pencil

• Your textbook

• A water bottle

• The teacher

Answer explanation

Inertia is the resistance of an object to changes in its state of motion. The teacher, being a person, has significantly more mass than a pencil, textbook, or water bottle, thus exhibiting the most inertia among the options.

Carl and Juan are playing catch. Carl throws a fastball to Juan and it hurts Juan’s hand. Why is this the case?

• Greater the acceleration, greater the force

• Greater the mass, greater the acceleration

• Greater the acceleration, the less the force

• Greater the mass, the less the force

Answer explanation

Carl's fastball likely hurt Juan's hand because of Newton's second law: greater acceleration results in greater force. The faster the ball is thrown, the more force it exerts on impact, causing pain.

James is on a paddleboard. He exerts a force on the water with the paddle, causing the water to move. The paddleboard also moves, but in the opposite direction. Which statement best explains why this happens?

• Inertia

• Action and reaction forces

• Newton’s 2nd Law of motion

• Law of Conservation of Momentum

Answer explanation

The paddle exerts a force on the water (action), and the water exerts an equal and opposite force on the paddleboard (reaction). This is described by Newton's third law of motion, which explains the movement in opposite directions.

Emma drops a watermelon from rest straight down from a tall building. Air resistance can be ignored. Which statement about the watermelon’s motion is FALSE?

• The watermelon falls at a constant velocity.

• The watermelon has a positive acceleration.

• The watermelon’s acceleration due to gravity is 9.8 m/s².

• The watermelon speeds up as it falls.

Answer explanation

The statement 'The watermelon falls at a constant velocity' is false because it starts from rest and accelerates due to gravity, increasing its speed until it hits the ground.

Henry is carrying a backpack with a mass of 95 kg. What is the weight of the backpack?

• 95 kg

• 95 N

• 931 kg

• 931 N

Answer explanation

Weight is calculated using the formula: weight = mass × gravity. Here, mass = 95 kg and gravity ≈ 9.81 m/s². Thus, weight = 95 kg × 9.81 m/s² = 931 N. Therefore, the correct answer is 931 N.

Priya is pushing a box with 16 N of force to the right, while Abigail is pushing the same box with 16 N of force to the left. Additionally, Rohan is applying 4 N of force downward on the box. What is the net force on the box?

• 36 N

• 4 N downward

• 32 N

• 16 N to the left

Answer explanation

The forces to the right and left (16 N each) cancel each other out, resulting in 0 N horizontally. The only unopposed force is 4 N downward, making the net force 4 N downward.

Noah is driving a 700 kg car with an acceleration of 5 m/s² down the interstate. What is the force required to accelerate the car?

• 3,500 N

• 650 N

• 14 N

• 0.071 N

Answer explanation

To find the force required to accelerate the car, use Newton's second law: F = m * a. Here, m = 700 kg and a = 5 m/s². Thus, F = 700 kg * 5 m/s² = 3,500 N, which is the correct answer.