Question

A car increases the speed from 20km/h to 50km/h in 10 sec. What's is acceleration

Answer 1

A car increases the speed from 20km/h to 50km/h in 10 sec. The acceleration is 3m/s

Answer 2

Initial velocity of the car = 20 km/hr

Converting into si unit

Initial velocity = 20*5/18 = 100/18 m/sec

Similarly
Final velocity = 50 km/hr
In si units
Final velocity = 50*5/18 = 250/18 m/sec

Now
Time given did change = 10 seconds

So,

Acceleration =( v-u) /t
So,

Acceleration =
$\frac{( \frac{250}{18} - \frac{100}{18} ) }{10} \\ \\ = \frac{ \frac{150}{18} }{10} \\ \\ = \frac{150}{180} = \frac{15}{18} = \frac{5}{6} = 0.83333..$
So,

The acceleration is 0.8333... M/sec²

Rounding off

Acceleration is equal to 0.84 m/sec²