Question

If a truck is moving with velocity 40 km/hr applies brakes to save a child at 25 m standing from the point from where brake is applied. If the time taken to stop the truck is 2 sec. Will the truck kill the child?​

Answer 1

Given:

Truck is moving with velocity 40 km/hr applies brakes to save a child at 25 m standing from the point from where brake is applied. If the time taken to stop the truck is 2 sec.

To find:

If the truck will hit the child or not?

Calculation:

Initial velocity of truck be u ;

$\rm{u = 40 \: km {hr}^{ - 1} = 40 \times ( \dfrac{5}{18} ) = 11.11 \: m {s}^{ - 1} }$

Now , let acceleration be a ;

$\rm{ \therefore \: a = \dfrac{v - u}{t} }$

$\rm{ = > \: a = \dfrac{0 - 11.11}{2} }$

$\rm{ = > \: a = - 5.55 \: m {s}^{ - 2} }$

So, distance travelled before stopping be d;

$\rm{\therefore\:{v}^{2} = {u}^{2} + 2ad}$

$= > \rm{{(0)}^{2} = {(11.11)}^{2} + 2( - 5.55)d}$

$\rm{ = > 11.11d = {(11.11)}^{2} }$

$\rm{ = > d = 11.11 \: m}$

Since d < 25 m , so the child will be saved.