Mechanical Aptitude Forces and Motion Principles Questions and Answers — Questions and Answers
Question 1: An object is moving at a constant velocity of 15 m/s. According to Newton's First Law of Motion, which of the following must be true?
- The object will eventually slow down due to inertia.
- The net force acting on the object is zero. (Correct answer)
- A constant force is required to maintain its velocity.
- The object's acceleration is 15 m/s².
Correct answer: The net force acting on the object is zero.
Newton's First Law, the law of inertia, states that an object in motion will stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. If the velocity is constant, it means the acceleration is zero. According to Newton's Second Law (F=ma), if acceleration (a) is zero, the net force (F) must also be zero.
Question 2: A mechanic uses a long wrench to loosen a tight bolt. Why is it more effective to apply force at the end of the wrench's handle rather than closer to the bolt?
- It increases the force applied to the bolt.
- It increases the torque applied to the bolt. (Correct answer)
- It reduces the friction between the bolt and the wrench.
- It decreases the wrench's moment of inertia.
Correct answer: It increases the torque applied to the bolt.
Torque is the rotational equivalent of force and is calculated as Force × Distance from the pivot point (the bolt). By applying force at the end of the handle, the mechanic maximizes the distance, which in turn maximizes the torque applied to the bolt, making it easier to turn.
Question 3: If a person is in an elevator that is accelerating upwards, their apparent weight will be:
- Less than their actual weight.
- Equal to their actual weight.
- Greater than their actual weight. (Correct answer)
- Zero.
Correct answer: Greater than their actual weight.
When the elevator accelerates upward, the floor must push up on the person with a force greater than their weight to overcome inertia and cause the upward acceleration. This increased normal force is what a scale measures, so their apparent weight increases.
Question 4: Which of the following best describes the difference between centripetal force and centrifugal force?
- Centripetal force is a real force pulling an object towards the center of rotation, while centrifugal force is an apparent outward force. (Correct answer)
- They are equal and opposite forces that cancel each other out.
- Centrifugal force is the force that keeps an object moving in a circle.
- Centripetal force only applies to objects in a vacuum, while centrifugal force applies everywhere.
Correct answer: Centripetal force is a real force pulling an object towards the center of rotation, while centrifugal force is an apparent outward force.
Centripetal force is a real, center-seeking force that is required to keep an object moving in a circular path. Examples include tension in a string or gravity. Centrifugal force is an apparent, or 'fictitious', force that an object seems to experience from its own rotating frame of reference, pushing it outward. It's a consequence of inertia.
Question 5: A 100 kg box is pushed across a floor with a constant force. If the force of friction opposing the motion is 50 Newtons, what is the net force required to accelerate the box at 2 m/s²?
- 150 N
- 200 N
- 50 N
- 250 N (Correct answer)
Correct answer: 250 N
First, calculate the force needed for acceleration using Newton's Second Law (F=ma): F_accel = 100 kg * 2 m/s² = 200 N. To achieve this acceleration, the applied force must overcome the friction and also provide the force for acceleration. Therefore, the total applied force is the sum of the force of friction and the acceleration force: 200 N + 50 N = 250 N.
Question 6: Two gears are in mesh. Gear A has 15 teeth and Gear B has 30 teeth. If Gear A rotates clockwise, what will happen to Gear B?
- It will rotate clockwise at twice the speed.
- It will rotate counter-clockwise at half the speed. (Correct answer)
- It will rotate clockwise at half the speed.
- It will rotate counter-clockwise at twice the speed.
Correct answer: It will rotate counter-clockwise at half the speed.
When two gears are in mesh, they rotate in opposite directions. Since Gear A is clockwise, Gear B must rotate counter-clockwise. The speed ratio is inversely proportional to the number of teeth. Gear B has twice as many teeth as Gear A, so it will rotate at half the speed of Gear A.
Mechanical Aptitude Forces and Motion Principles Questions and Answers
An object is moving at a constant velocity of 15 m/s.
According to Newton's First Law of Motion, which of the following must be true?