Chapter 2: Forces Quiz

Explanation
Friction acts in the opposite direction to the direction of an object's motion. When an object moves, friction acts in the opposite direction to the motion, trying to slow down or stop the object's movement. This is because friction is a force that opposes the relative motion between two surfaces in contact. Therefore, the correct answer is "opposite".

Explanation
Inertia is the property of an object to resist any change in its state of motion. According to Newton's first law of motion, an object at rest will remain at rest unless acted upon by an external force. This is because the object possesses inertia, which causes it to resist any change in its state of rest. Therefore, unless a force is applied to overcome the object's inertia, it will continue to stay at rest.

Explanation
The correct answer is 5000 N because the force required to accelerate an object can be calculated using the formula F = m*a, where F is the force, m is the mass, and a is the acceleration. In this case, the mass of the ball is 10 kg and the acceleration is 500 m/s^2. Plugging these values into the formula, we get F = 10 kg * 500 m/s^2 = 5000 N. Therefore, a force of 5000 N is required to accelerate the 10-kg ball at a rate of 500 m/s^2.

Explanation
The momentum of an object is calculated by multiplying its mass by its velocity. In this case, the mass of the car is given as 1500 kg and its velocity is given as 10 m/s. Therefore, the momentum of the car is 1500 kg multiplied by 10 m/s, which equals 15,000 kg x m/s.

Explanation
An unbalanced force can cause an object's motion to change. When there is an unbalanced force acting on an object, it means that the forces acting on the object are not equal in magnitude and opposite in direction. This imbalance causes the object to accelerate or decelerate, or change its direction of motion. In contrast, a balanced force occurs when the forces acting on an object are equal in magnitude and opposite in direction, resulting in no change in motion. Inertia and mass are properties of an object and do not directly cause a change in motion.

Explanation
Mass refers to the amount of matter in an object. It is a fundamental property of an object and is independent of its location or the force acting upon it. Weight, on the other hand, is the force exerted on an object due to gravity and can vary depending on the gravitational pull. Inertia is the resistance of an object to changes in its motion. Therefore, the correct answer is mass, as it specifically relates to the amount of matter in an object.

Explanation
Newton's second law of motion states that the force acting on an object is directly proportional to the mass of the object and the acceleration it experiences. In other words, the force equals the product of mass and acceleration. This means that the greater the mass of an object or the greater the acceleration it experiences, the greater the force acting on it will be. Conversely, if the mass or acceleration decreases, the force will also decrease. Therefore, the correct answer is "force equals mass times acceleration."

Explanation
Centripetal force is the correct answer because it is the force that causes objects to move in a circle. It acts towards the center of the circle and keeps the object in circular motion. This force is necessary to counterbalance the tendency of the object to move in a straight line due to inertia. Without centripetal force, objects would continue in a straight line instead of following a circular path.

Explanation
An object in free fall accelerates until it reaches terminal velocity. This is because in free fall, the object is only under the influence of gravity, which causes it to accelerate downwards. As the object falls, its speed increases until it reaches a point where the upward force of air resistance balances out the downward force of gravity. At this point, the object stops accelerating and reaches a constant velocity known as terminal velocity. Therefore, the correct answer is "accelerates".

Explanation
Forces can be added together only if they are acting on the same object. When forces act on different objects, they cannot be added together because they are exerted on separate entities and have different effects. Therefore, the statement is false.

Explanation
According to Newton's second law of motion, the acceleration of an object is directly proportional to the net force applied to it and inversely proportional to its mass. This means that if the force acting on an object increases, and its mass remains constant, the acceleration of the object will also increase. Therefore, the statement that acceleration increases as force increases, if mass stays the same, is true.

Explanation
The statement is true because gravity is a force that attracts objects towards each other. The strength of the gravitational force between two objects depends on their masses and the distance between them. As the distance between two objects decreases, the force of gravity between them increases. Therefore, if two objects are closer to each other, the force exerted by gravity will be stronger.

Explanation
The statement that the force of friction acts between all objects in the universe is false. Friction is a force that opposes the relative motion between two surfaces in contact. While friction is a common force that we experience in our daily lives, it is not present between all objects in the universe. In space, for example, where there is no atmosphere or surfaces in contact, there is no friction. Additionally, friction only occurs when there is relative motion or an attempt to move between two surfaces, so it does not act between all objects.

Explanation
A satellite in orbit around Earth is constantly being pulled towards Earth by gravity. However, it is also moving forward with enough speed that it continuously falls around the Earth instead of crashing into it. This is known as freefall or gravitational attraction. As a result, the statement is true.

Explanation
This statement is false because the scenario described in the question does not involve unbalanced forces. Unbalanced forces occur when there is a net force acting on an object in a particular direction, causing it to accelerate or move. In this case, both boys pulled with equal strength and neither of them moved, indicating that the forces were balanced.

Explanation
This scenario aligns with Newton's first law of motion, also known as the law of inertia. According to this law, an object in motion will continue to move in the same direction and at the same speed unless acted upon by an external force. In this case, Patty was walking quickly through the cafeteria (in motion) when she tripped over a broomstick (external force). As a result, she flew forward along with all of her food, demonstrating the concept of inertia. Therefore, the answer is true.