#
**21) **A ball is dropped from a height of 10 m on a smooth floor and after the impact the ball bounces to a height of 2.5 m. The coefficient of restitution between the ball and the floor is

**Answer is:**

## 0.5

**Related ISRO Technical Assistant Mechanical Question Paper - 2017 with Answer Key**

**Answer is:**

### Remains constant

**Answer is:**

### Surface tension force

**Explanation:**

The important dimensionless numbers in fluid mechanics are

1. Reynold’s number

2. Froude’s number

3. Weber’s number

4. Euler’s number

5. Mach’s number or Cauchy’s number

**Reynold’s number**: Reynold’s number is the ratio of inertia force to the viscous force.

**Froude’s number**: Froude’s number is the ratio of inertia force to the gravity force.

**Weber’s number**: Weber’s number is the ratio of inertia force to the surface tension force.

**Euler’s number**: Euler’s number is the ratio of inertia force to the pressure force.

**Mach’s number or Cauchy’s number**: Mach’s number or Cauchy’s number is the ratio of inertia force to the elastic force.

**Answer is:**