Question

Label these as balanced or unbalanced:

Answer 1

Answer:

1. A book lying on a table  - Balanced force
2. An airplane cruising in level flight  - Balanced
3. A rock falling from a cliff  - Unbalanced force
4. A bridge collapsing in an earthquake  -  Unbalanced force
5. A man sitting on a park bench  - Balanced force
6. A space shuttle taking off  - Unbalanced force
7. A car maintaining a constant speed on a straight road  - Balanced force
8. An airplane landing - Unbalanced force

Explanation:

Usually, one or more forces act on a body at an instant of time. When these forces acting on a body and bring the body in the equilibrium position, the force is said to be balanced. The unbalanced force changes the equilibrium state of the body.

As in the case of an airplane cruising in a level flight, the weight of the plane will be equal to the lift force and the thrust is equal to the drag. So the plane is experiencing a balanced force.

Answer 2

Answer:

1. A book lying on a table  (Balanced force)  

2.An airplane cruising in level flight (Balanced force)

3.A rock falling from a cliff (Unbalanced force)

4.A bridge collapsing in an earthquake (Unbalanced force)

5.A man sitting on a park bench (Balanced force)  

6.A space shuttle taking off (Unbalanced force)

7.A car maintaining a constant speed on a straight road (Balanced force)

8.An airplane landing (Unbalanced force)

Explanation:

An object will be in equilibrium or balanced state if the sum off all the forces and toques on that object will be equal to zero.  

in case of book lying on the table its weight is balanced by the normal force exerted by the table. So, balance force is acting on it. Same analogy can be applied to a man sitting on bench.  

When air plane cruise in level flight, the weight of airplane is equal to the lift force and drag force is equal to the thrust force. Hence, balanced force acts on the airplane.

When car runs with the uniform speed on the road, engine force is equal to the frictional force. Hence, balanced force acts on the car.  

In all other cases unbalance forces act which can be judged just by looking statements.