Question

A car increases its speed from 20 km/h to 50 km/h in 10 seconds. Its acceleration is
A) 30 $m/{s^2}$
B) 3 $m/{s^2}$
C) 18 $m/{s^2}$
D) None

Answer 1

Find change in velocity with respect to time that is called acceleration. Change in velocity can be calculated by subtracting initial velocity with final velocity. And then divide this change in velocity by time.

Complete step by step solution:
Given-
Final velocity, v = 50 km/h
Initial velocity, u = 20 km/h
Time taken, t = 10 sec
So the change in velocity can be calculated as
$v - u = \left( {50 - 20} \right)$km/hr
= 30 km/hr
On converting the units into m/s
We get,
= 30 km/hr $\Rightarrow \dfrac{{30 \times 1000}}{{60 \times 60}} \Rightarrow \dfrac{{25}}{3}$ m/s
We know the acceleration formula,
$a = \dfrac{{\left( {v - u} \right)}}{t}$
Put the value of change in velocity and time in above formula
we get,
=$\dfrac{{25}}{3} \times \dfrac{1}{{10}}$
$= \dfrac{5}{6}$ m/$s^2$
There is no such option.

So the correct answer is option D (none)

Additional Information: Velocity of the body increases with time then acceleration formed and if the velocity of the body decreases then retardation formed
So we say that negative acceleration is called retardation
If a body moving with a constant velocity therefore change in velocity is zero . Then the acceleration is also zero.

Note: Students be aware here in this question the initial and final speed is given in km/h while time in second. So first we need to convert all parameters in the same unit then select the correct option because this is an objective type question.