A truck starts from rest and rolls down a hill with constant acceleration. It travels a distance of 400 m in $20\ s$. Find its acceleration. Find the force acting on it if its mass is $7\ tonnes\ (Hint:\ 1\ tonne = 1000\ kg.)$

AcademicPhysicsNCERTClass 9

Given:

A truck starts from rest and rolls down a hill with constant acceleration. It travels a distance of 400 m in $20\ s$.

To do:

To find its acceleration. Find the force acting on it if its mass is $7\ tonnes$.

Solution:

Here, as given initial velocity $u=0$

Distance covered $s=400\ m$

Time $t=20\ s$

Mass of the truck $7\ tonnes=7\times 1000\ kg.=7000\ kg.$

Calculation of the acceleration:

Let us use the third equation of the motion to find the acceleration of the truck:

$s=ut+\frac{1}{2}at^2$ 

$400=0+\frac{1}{2}\times a\times (20)^2$

Or $400=\frac{400a}{2}$

Or $a=\frac{400\times2}{400}$

Or $a=2\ ms^{-2}$ 

Calculation of force acting on the truck:

Let us calculate the force that is acting upon the truck by using newtons second law of motion

$F=ma$

$=7000\times 2$

$=14000\ N$

Therefore, the acceleration of the truck is $2ms^{-2}$, and a force of $14000\ N$ is acting upon the truck.

raja
Updated on 10-Oct-2022 13:22:30

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