Question

State which of the following situations are possible and give an example for each of these:
(a) An object with a constant acceleration but with zero velocity.
(b) An object moving in a certain direction with an acceleration in the perpendicular direction.

Answer 1

Hint
The free fall object moved by the force of gravity, possesses acceleration due to gravity but has the velocity zero. If the force is rotational force, then the direction that the object moves and the direction of the acceleration acts will be in perpendicular.

Complete step by step answer
Velocity is defined as the rate of change of displacement with respect to time. Whereas the acceleration is defined as the changing of the velocity over time. So when the velocity of the object is changing, then the object is said to be acceleration. However the acceleration depends on the velocity, there are some cases in which the acceleration can act due to some external force like gravity, magnetic and other forces.
(a) Gravitation force is the kind of the attractive force of the earth that attracts the objects towards its surface. The example for this type of condition is, if a stone is thrown towards the sky, the stone moves upward with a certain velocity and when the force on the stone gets over, it stops its movement. Then it moves downward with the zero velocity acting on it but with the acceleration as . This is due to the gravity that provides the constant acceleration to the stone.

(b) In a rotational motion, the force acting on the object that undergoes the motion may be centripetal force or the centrifugal force. In centripetal force, the force acts towards the center. Whereas in centrifugal force, the force acts away from the center of the rotation. The example for this condition is the ball is made tied to the thread which is hanged. Then it is made rotated horizontally with the centripetal force. Here the object moves in the one direction, but its acceleration always moves at right angles to the ball towards the center.
Hence both the situations are possible.

Note
Remember that gravitational force always acts downward and is constant at all points on the earth. This is the reason that the stone reaches earth with the acceleration even though its velocity is zero. In the process of rocket launching, the rocket is provided with the fuel to overrun the earth's gravitational force.