A solid sphere falls with a terminal velocity of 20 m s−1 in air. If it is allowed to fall in vacuum,
(a) terminal velocity will be 20 m s−1
(b) terminal velocity will be less than 20 m s−1
(c) terminal velocity will be more than 20 m s−1
(d) there will be no terminal velocity
Answers
If it is allowed to fall in vacuum, there will be no terminal velocity. Option d is correct.
Explanation:
1. Terminal velocity is maximum velocity is attained with constant value. For constant value of velocity, there must be no net force acting on object.
2. In first case
Sphere falls in air due to gravity force. Gravity force act in downward direction.
3. Sphere motion in downward direction, due to fluid friction air oppose motion of sphere. Direction of resistant force by air is in opposite to motion. So direction of opposing force by air is in upward direction.
4. Here we see that there are two force on sphere. one is in downward direction while other in upward direction.
5. Terminal Velocity of sphere is velocity of sphere when upward force is equal to downward force, Its means net force on object is zero.
6. But in case, when sphere fall in vacuum.
In this case there are only one force in downward direction which is gravitational force.
7. There are not possible to net force become zero in vacuum. So it is talking about terminal velocity is meaning less or we say that there will be no terminal velocity.