A car is travelling at a constant speed of 30m s -1 on
the road when a kangaroo crosses in front of the car at a distance of 65 m away. The driver takes 0.6 seconds to hit the brakes and then she decelerates with a constant deceleration 10.0 m s -2
Calculate how fast the car is travelling in m s.

Respuesta :

The car hits the kangaroo at a velocity of 6.3 m/s.

Explanation:

In the first 0.6 seconds (reaction time), the car continues travelling at a constant velocity of

u = 30 m/s

Therefore, since the time interval is

t = 0.6 s

It means that the car covers a distance of

[tex]d_1 = ut=(30)(0.6)=18 m[/tex]

The initial distance from the kangaroo was

D = 65 m

Therefore, the distance left to the kangaroo is

[tex]d=D-d_1 = 65-18=47 m[/tex]

In this second part, the car travels with a uniformly accelerated motion, therefore we can use the suvat equation

[tex]v^2-u^2 = 2ad[/tex]

where:

v is the final velocity of the car when it reaches the kangaroo

u = 30 m/s is the initial velocity

[tex]a=-10 m/s^2[/tex] is the deceleration

s = 47 m is the distance to be cover

Solving for v, we find:

[tex]v=\sqrt{u^2+2ad}=\sqrt{30^2+2(-10)(47)}=6.3 m/s[/tex]

So, the velocity of the car when it hits the kangaroo is 6.3 m/s.

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