Question

A car increase its speed from 20km/hr to 50km/hr in 10sec find acceleration

Answer 1

change in speed = 50-20 = 30 km/ hr
in m/s this is
$30 \frac{km}{hr} \: \times \frac{5}{18} = \frac{25}{3} \frac{m}{s}$
time taken= 10 sec

acceleration is given by
$\frac{change \: in \: speed}{time \: taken \: } = \frac{25}{3} \div 10 = \frac{5}{6} \frac{m}{s} \: = 0.83 \frac{m}{s}$