# Physics Questions and Answers – Laws of Motion – Equilibrium of a Particle

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This set of Physics Online Test for NEET Exam focuses on “Laws of Motion – Equilibrium of a Particle”.

1. The first condition of equilibrium of a body is ___
a) Sum of all force on a body should be zero
b) Sum of all moments on a body should be zero
c) Sum of the initial and final force should be zero
d) Relative difference of forces should be zero

Explanation: The first condition for a body to exist in equilibrium is that the sum of all forces on the body must be zero. Which means that the resultant force on a body should be zero.

2. The second condition of equilibrium of a body is ___
a) Sum of all force on a body should be zero
b) Sum of all moments on a body should be zero
c) Sum of the initial and final force should be zero
d) Relative difference of forces should be zero

Explanation: The second condition for a body to exist in equilibrium is that the sum of all moments on the body must be zero. Which means that the resultant moment on a body should be zero.

3. What can be said about a body which is moving with a constant velocity?
a) It is in static equilibrium
b) It is in dynamic equilibrium
c) It is in the state of non-equilibrium
d) Its distance is conserved

Explanation: When a body is moving with constant velocity, there is no net force or moment acting on it. Hence, the body is in equilibrium. But since the body is moving, the equilibrium is known as dynamic equilibrium. Static equilibrium occurs when the body is at rest.
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4.Two forces are acting on a body. For the body to remain in equilibrium, the forces have to be ____
a) Equal in magnitude and opposite in direction
b) Equal in direction and opposite in magnitude
c) In the same direction
d) In perpendicular directions

Explanation: Only when the forces are equal in magnitude and opposite in direction, the net force will be zero on the body. Since there is no moment, we need not care about the second condition of equilibrium. The body is in equilibrium only when the net force acting on it is zero which is satisfied only in this manner.

5. Two forces act on a ball. One of the forces is positive and acts towards right, the other one acts towards left and is ______
a) Negative
b) Positive
c) Neutral
d) Having a magnitude of 5 N

Explanation: The force has to be positive. The reason is that the forces are acting in opposite directions. Which means that the direction of the forces has been specified and they are bound to cancel each other out. So, if, the second force is negative, the net direction will be towards right and the body will not be able to stay in equilibrium.

6. Two forces act on a body. One of them is 7î – 13ĵ. What is the value of the other force?
a) 7î – 13ĵ
b) -7î + 13ĵ
c) 7î + 13ĵ
d) -7î – 13ĵ

Explanation: For the body to remain in equilibrium, the total force on it should be zero. As one of the forces is given, the other force can be found out by subtracting it from zero. Hence the answer is -7î + 13ĵ.

7. Three forces act on a body. Two of them are 7î – 13ĵN and 2î – 11ĵ. What is the value of the other force?
a) -9î + 24ĵ
b) -24î + 9ĵ
c) 24î + 9ĵ
d) -9î – 24ĵ

Explanation: For the body to remain in equilibrium, the total force on it should be zero. As two of the forcesare given, the other force can be found out by subtracting the sum of both the given forces from zero. Hence the answer is -9î + 24ĵ.

8. If a body returns to its original state of equilibrium after giving it a small displacement, the equilibrium is known as ______
a) Stable equilibrium
b) Unstable Equilibrium
c) Neutral Equilibrium
d) Simple equilibrium

Explanation: The body is said to be in the state of stable equilibrium if it returns to its original equilibrium after giving it a slight displacement. In unstable equilibrium, the body does not return to its original equilibrium and moreover also does not achieve any other equilibrium. In neutral equilibrium, the body attains a new equilibrium every time it is displaced.

9. A set of forces are acting on a body in equilibrium. Which one of the following is true?
a) The vector sum of the forces is zero
b) The scalar sum of the force is zero
c) All the forces are zero
d) All the forces are equal and opposite in direction to each other

Explanation: When a body is in equilibrium, the sum of all the forces is zero. The sum of all the forces relates to the vector sum of all the forces and not any other sum. The scalar sum is always positive hence it cannot be zero. The forces need not be zero for the body to be in equilibrium, only the vector sum has to be zero. The same goes with the magnitude and direction of the forces.