Physics, 02.08.2019 04:40 cutielove2912

Acar traveling at 20 minutes/seconds when the driver sees a child standing in the road. he takes 0.80 seconds to react, 10 steps on the brakes and slows at 7.0 m/s square. how far does the car go before it stops?

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Answer from: dondre54

I assume you mean 20 m/s.

In the first 0.80 seconds, the car travels:

20*0.80 = 16 m

During the period of deceleration, you can calculate the distance travelled using:

$v^{2} = u^{2} + 2as$ where s is the distance travelled, v is the final speed (0), u is the initial speed (20 m/s), and a is the acceleration (-7.0 m/s^2).

This gives:

2*7.0s = 20^2
14.0s = 400
s = 400/14 m

The total distance the car travels is:

16 + 400/14 = 44.6 m (3 s.f.)

Answer from: Quest

The answer is d) by requesting advice on science internet sites

Answer from: Quest

force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

$f\alpha \frac{dp}{dt}$

⇒ $f= k \frac{dp}{dt}$

here k is the proportionality constant whose value is 1.

$f=\frac{dp}{dt}$

$f= \frac{d[mv]}{dt}$

$f= m\frac{dv}{dt} +v\frac{dm}{dt}$

$f=ma+v\frac{dm}{dt}$ [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.

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Acar traveling at 20 minutes/seconds when the driver sees a child standing in the road. he takes 0.8...