Answer:
Average speed, 
Explanation:
Given:
- Initial speed, u=40 cm/s
- final speed , v=20 cm/s
- Time taken, t=5 s
<u>First case</u>
Using equation of motion we have
Now using,
now putting the value of a in first equation we get
<u>Second case</u>
Acceleration
Time taken 
using equation of motion in one Dimension we have
Average speed is equal to total distance travelled per unit total time taken
Hooke’s law of elasticity states that, for relatively small deformations of an object, the displacement or size of the deformation is directly proportional to the deforming force or load. Under these conditions the object returns to its original shape and size upon removal of the load. Elastic behavior of solids according to Hooke’s law can be explained by the fact that small displacements of their constituent molecules, atoms, or ions from normal positions is also proportional to the force that causes the displacement.
