Physics, 06.09.2019 02:20 hernan99961

An object is shot vertically upward into the air with a positive initial velocity. what correctly describes the velocity and acceleration of the object at its maximum elevation?
velocity acceleration
(a) positive positive
(b) zero negative
(c) positive negative
(d) zero zero
(e) negative negative

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Answer from: stephaniedoffing

option (B)

Explanation:

According to the vector analysis, the upward direction is taken as positive and the downward direction is taken as negative.

Similarly, the rightward direction is taken as positive while the leftward direction is taken as negative.

As the object is hot vertically upwards so the direction of velocity is taken as positive as given in the question.

At the maximum height, the velocity is zero.

The acceleration acting on the object is acceleration due to gravity which is always acting downwards so it is taken as negative.

Thus, option (B) is true.

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.

Answer from: Quest

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