Newton’s Laws of Motion MCQs

Answer: The elevator may be going up or down with uniform speed. The net force acting on the elevator is given by the equation$$ T \ – \ mg \ = \ ma$$
The tension and the weight of the elevator can only be equal if the net acceleration of the lift is zero. Net acceleration is zero if the body is at rest or the change in velocity of the body is zero. In uniform speed, there is no change in velocity. Thus, there is ero acceleration and the statement is true. We do not consider the direction of the elevator in this case.

Answer: All of the above statement are true.

Statement 1: At the top of the trajectory of a projectile motion, the vertical velocity of a particle is zero however, it is still accelerating under constant acceleration due to gravity.

Statement 2: Speed is a scalar quantity and velocity is a vector quantity. Therefore, speed is always equal to or greater than the magnitude of velocity.

Statement 3: In a horizontal projectile, the vertical component of velocity is 0. So, in both the cases, the bodies are in a state of free fall. Thus, they will reach the ground simultaneously when dropped from the same height.

Answer: They have different force.

As the bodies are let fall, they are in a state of freefall. During freefall, each body is acted upon by a constant downward acceleration equal to the acceleration due to gravity (g) of the Earth.

Also, they have no initial velocity so, their time of descending will also be the same, i.e., h = 1/2 gt², if they are left from the same height.

However, the Force (F) acting on them is given by mass times acceleration. The mass of both bodies being different, the Force acting on them is also different.

Answer: The terminal velocity of an object thrown upward is 0 m/s.

Any object in the Earth’s atmosphere, when thrown upward is acted by a constant downward acceleration equal to ‘g’. As the body’s motion is in opposite direction to the acceleration, the body’s velocity continuously slows down. It finally stops when it reaches the maximum height where its velocity is 0 m/s. Furthermore, it cannot ascend so, it starts to descend in the direction of g.