Physics, 21.12.2019 01:31 Karxra

Afully loaded, slow-moving freight elevator has a cab with a total mass of 1700 kg, which is required to travel upward 45 m in 2.1 min, starting and ending at rest. the elevator's counterweight has a mass of only 840 kg, so the elevator motor must pull the cab upward. what average power is required of the force the motor exerts on the cab via the cable?

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Answer from: drea445

3,010 W

Explanation:

mass of elevator (Me) = 1700 kg

mass of counter weight (Mc) = 840 kg

travel distance (d) = 45 m

time (t) = 2.1 min = 126 s

What average power is required of the force the motor exerts on the cab via the cable?

from Newtons second law of motion

force exerted by the elevator motor + force exerted by the elevator counter weight = force exerted by the elevator cab weight

therefore

force exerted by the elevator motor = force exerted by the elevator counter weight - force exerted by the elevator cab weight

force exerted by the elevator motor (Fm) = (Me x g) - (Mc x g)

force exerted by the elevator motor (Fm) = (1700 x 9.8) - (840 x 9.8)

force exerted by the elevator motor (Fm) = 8428 N

average power exerted by the motor = Fm x speed

where speed = distance / time

average power exerted by the motor = Fm x (distance / time)

average power exerted by the motor = 8428 x (45/126) = 3,010 W

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

well clustered together.

points close on a scatter diagram

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Afully loaded, slow-moving freight elevator has a cab with a total mass of 1700 kg, which is require...

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