Bissoy.com
Doctors Medicines MCQs Q&A

If a block of mass m placed inside elevator moving upward at constant speed,then the magnitude of normal force 

If a block of mass m placed inside elevator moving upward at constant speed,then the magnitude of normal force  Correct Answer equal to mg.

Correct option-3

Concept:-

Sir Isaac Newton has given three laws to describe the motion of an object. These laws are known as Newton's laws of motion.

1) NEWTON'S FIRST LAW OF MOTION:-

  • A body that continues to its state of rest will remain in uniform speed in a straight line unless and until it is compelled by an external force to change its state of rest or of uniform motion.
  • Newton's first law recognizes that everybody has some inertia.
  • Inertia is an intrinsic property of the body by the virtue of which it resists a change in its state of rest or of uniform motion.

2) NEWTON'S SECOND LAW OF MOTION:-

  • The net force applied to a body is equal to the rate of change of momentum.
  • For the case of mass, force equals mass times acceleration.
  • i.e. F = ma

Where,

  •  F = force applied
  • m = mass and
  • a = acceleration.
  • Unlike Newton’s first law of motion, Newton's second law of motion pertains to the behavior of objects for which all existing forces are unbalanced.
  • Newton's second law of motion is more quantitative and is used extensively to calculate what happens in situations involving a force.

3) NEWTON'S THIRD LAW OF MOTION:-

  • It states that to every action there will be an equal and opposite reaction.
  • i.e. “when one object exerts a force on the other object, the first object experiences a force which is equal in magnitude in the opposite direction of the force which is exerted”.

 

Calculation:-

  • Imagine that a box is placed in an elevator.

  • From (FBD) free-body diagrams, the elevator by itself, and the combined system of the box plus the elevator.

 

  • FBD (Free-Body Diagram)

    • A free-body diagram is a diagram of a given system that is the one in which we represent all the forces acting on it and thus we calculate the net force.
    • Free-body diagrams are used to show the direction and magnitude of all the forces acting upon an object.
    • The length of the arrow in FBD represents the magnitude of the force and arrows are labeled to indicate the type of force.
    • In these diagrams, the object is generally represented like a box and the arrows representing force are drawn from the center of the object.
    • There is no strict rule on the number of forces that can be drawn in a free-body diagram.
    • For an example of a book placed at rest on the ground, figure (b) is given below.

    ​[ alt="4012" src="//storage.googleapis.com/tb-img/production/21/05/4012.png" style="width: 186px; height: 239px;">

Related Questions

An elevator with a mass of 2500 kg rests at 10m above the base of an elevator. It is raised to 100m above the base. The elevator falls freely to the base and strikes a strong spring. Find the potential energy of the elevator, (g = 9.8 ms-2).
Three blocks with masses m, 2 m and 3 m are connected by strings, as shown in the figure. After an upward force F is applied on block m, the masses move upward at constant speed v. What is the net force on the block of mass 2 m? (g is the acceleration due to gravity)
What is the value of force measured by a force sensor lying on a plane ground if a block of mass 3 kg is kept on it and a normal upward tensile force of 5 Newton is applied on the block? (Take acceleration due to gravity=10m/s2)
What is the value of force measured by a force sensor lying on a plane ground if a block of mass 2 kg is kept on it and a normal upward tensile force of 4 Newton is applied on the block? (Take acceleration due to gravity=10m/s2)
A spring mass system is on a horizontal plane. Spring constant is 2N/m & mass of block is 2kg. The spring is compressed by 10cm and released. A small ball is released from a height of 2m above the block on the horizontal plane. At what time should the ball be left if the block is released from the extreme position at t=0, given that the ball has to fall on the block when the speed of block is maximum?
A block R of mass 100 kg is placed on a block S of mass 150 kg as shown in the figure. Block R is tied to the wall by a massless and inextensible string PQ. If the coefficient of static friction for all surfaces is 0.4, the minimum force F (in kN) needed to move the block S is
Mr. John is conducting elevator experiments. Bobby stands on a weigh scale and reads the scale while ascending and descending the building. Bobby’s mass is 80 kg. He notices that the scale readings depend on what the elevator is doing. Angular velocity of hour hand watch is double than that of Earth’s rotation. What is the scale reading when John accelerates upward at 0.40 m/s2?
Consider we have two blocks of masses P and Q. Now block Q was placed on top of P as shown in the figure below also there was no frictional force between mass P and surface of the plane whereas the friction force between P and Q can be given as f. In this case what will happen if we apply the force of magnitude F on block P (consider f < F)
An elevator can carry maximum of 16 passengers with an average weight of 80 kg. However, four boys more than the maximum carrying capacity of the elevator entered it making the average weight as 86 kg and overloading the elevator. What is the average weight of those four boys ?
A spring block system is on a horizontal surface. The block is compressed by 10cm. What should be the coefficient of friction between the block and ground such that the block comes to a stop at the mean position? Mass of block = 0.5kg & spring constant = 3N/m.