IMAT - International Medical Admissions Kinematics and Dynamics Questions and Answers — Questions and Answers
Question 1: A stone is thrown horizontally with a speed of 10 m/s from the top of a cliff that is 45 m high. Neglecting air resistance, how long does it take for the stone to reach the ground? (Use g = 10 m/s²)
- 4.5 s
- 1.5 s
- 3.0 s (Correct answer)
- 9.0 s
Correct answer: 3.0 s
The time of flight is determined solely by the vertical motion. The initial vertical velocity is zero. Using the kinematic equation s = ut + ½at², where s is the height (45 m), u is the initial vertical velocity (0 m/s), and a is the acceleration due to gravity (g ≈ 10 m/s²), we can solve for time t: 45 = (0)t + ½(10)t² which simplifies to 45 = 5t². Solving for t gives t² = 9, so t = 3.0 s.
Question 2: A book is resting on a horizontal table. According to Newton's Third Law of Motion, what is the reaction force to the gravitational force exerted by the Earth on the book?
- The gravitational force exerted by the book on the Earth. (Correct answer)
- The normal force exerted by the table on the book.
- The net force on the book, which is zero.
- The frictional force between the book and the table.
Correct answer: The gravitational force exerted by the book on the Earth.
Newton's Third Law states that for every action, there is an equal and opposite reaction, and these forces act on two different objects. The 'action' is the Earth exerting a gravitational force on the book. Therefore, the 'reaction' is the book exerting an equal and opposite gravitational force on the Earth.
Question 3: A 5 kg box is pulled 4 m up a frictionless ramp inclined at an angle of 30° to the horizontal. What is the work done against the force of gravity? (Use g = 10 m/s²)
- 200 J
- 173 J
- 50 J
- 100 J (Correct answer)
Correct answer: 100 J
The work done against gravity is equal to the change in the object's gravitational potential energy, calculated as W = mgh. The vertical height 'h' is found using trigonometry: h = d * sin(θ), where d is the distance along the ramp (4 m) and θ is the angle of inclination (30°). Thus, h = 4 * sin(30°) = 4 * 0.5 = 2 m. The work done is W = (5 kg) * (10 m/s²) * (2 m) = 100 J.
Question 4: Which of the following statements is always true for an inelastic collision between two objects in an isolated system?
- Kinetic energy is conserved, but momentum is not.
- Momentum is conserved, but kinetic energy is not. (Correct answer)
- Both kinetic energy and momentum are conserved.
- Neither kinetic energy nor momentum is conserved.
Correct answer: Momentum is conserved, but kinetic energy is not.
In any collision occurring in an isolated system (where no net external forces act), the total momentum is always conserved. An inelastic collision is defined as a collision in which kinetic energy is not conserved; some of it is transformed into other forms of energy, such as heat or sound.
Question 5: The velocity-time graph for an object's motion is a straight line passing through the origin with a positive slope. Which of the following correctly describes the object's motion?
- The object is at rest.
- The object is moving with constant velocity.
- The object is moving with constant positive acceleration. (Correct answer)
- The object is moving with increasing acceleration.
Correct answer: The object is moving with constant positive acceleration.
In a velocity-time graph, the slope of the line represents acceleration. A straight line indicates a constant slope, meaning the acceleration is constant. A positive slope indicates that the velocity is increasing at a constant rate, which is constant positive acceleration. Passing through the origin means the initial velocity was zero.
Question 6: A car of mass 1200 kg travels at a constant speed of 20 m/s around a flat, circular bend with a radius of 80 m. What is the magnitude of the centripetal force required to keep the car on this path?
- 6000 N (Correct answer)
- 300 N
- 2400 N
- 48000 N
Correct answer: 6000 N
The centripetal force required for an object to move in a circular path is given by the formula Fc = mv²/r, where m is the mass, v is the speed, and r is the radius of the circular path. Plugging in the given values: Fc = (1200 kg) * (20 m/s)² / 80 m = (1200 * 400) / 80 = 6000 N.
IMAT - International Medical Admissions Kinematics and Dynamics Questions and Answers
A stone is thrown horizontally with a speed of 10 m/s from the top of a cliff that is 45 m high.
Neglecting air resistance, how long does it take for the stone to reach the ground? (Use g = 10 m/s²)