Option 1 : 45 m/sec

**Given:**

Speeds of both cars = 80 km/hr, 82 km/hr

**Formula used:**

When two bodies move in opposite direction,

Relative Speed = Sum of Speeds

**Concept used:**

To convert a speed given in km/h into a speed in m/s, multiply with 5/18

**Calculation:**

According to the question:

Relative Speed = Sum of Speeds

⇒ Relative Speed = (80 + 82) km/hr = 162 km/hr

Change in m/sec,

⇒ [162 × (5/18)] = 45 m/sec.

**∴ The relative speed of the two cars are 45 m/sec.**

__Additional Information__

Distance covered = Speed × Time

- Units of Time, Speed and Distance
- The basic unit of time is a second, which could also be expressed in other units such as minutes (min) and hours (hr).
- The basic unit of speed is meter per second m/s, which could also be expressed in other units such as m/min or km/h.
- The basic unit of distance meter (m), which could also be expressed in other units such as kilometre (km).
- To convert a speed given in m/s into a speed in km/h, multiply with 18/5.
- To convert a speed given in km/h into a speed in m/s, multiply with 5/18.
- 1 km = 1000 m
- 1 min = 60 sec.

Average speed:

- 1. When a body travels different distances at different speeds, the average speed is the amount of time taken to travel the total distance in total time, Therefore, the formula for Time Speed Distance is:
- Average speed = Total distance/ Total time
- 2. When the body travels at speeds of u and v units for equal distances:
- Average speed = 2uv/(u + v)

Relative speed:

- Consider two bodies moving at speeds u and v.
- 1. When they are moving in the same direction, the relative speed between the two bodies is the difference of their speeds,
- (u – v) if u > v
- (v – u) if v > u.
- 2. When they are moving in the opposite directions, the relative speed between the two bodies is the sum of their speeds,
- (u + v)