Mwork = force × distance (w = fd) in which scenario is the most work done?
group of answer choices

a parrot lifts a cracker off the ground to eat.

a weighlifter holds a 150 pound barbell for 3 minutes.

a waiter holds a tray of 15 glasses of water over his head while standing at the front of a restaurant.

a truck motor runs for 24 hours while the truck is parked.

A parrot lifts a cracker off the ground to eat.

Explanation:

Work is said to be done by a force only if the force causes displacement.

Work (W) by a force (F) causing a displacement (d) is given as:

Displacement of an object is the net change in its position and a body that is not moving has zero displacement.

Let us check each option now.

Choice 1:

A parrot lifts a cracker off the ground to eat.

Here, the lifts a cracker off the ground. So, the parrot applies some force on the cracker and the cracker's position has changed.

So, there is work done by the parrot as force causes a displacement.

Choice 2:

A weightlifter holds a 150 pound barbell for 3 minutes.

Here, no work is done as the force applied to hold the barbell is not producing any displacement.

Choice 3:

A waiter holds a tray of 15 glasses of water over his head while standing at the front of a restaurant.

Here, no work is done as the force applied to hold the glasses of water is not producing any displacement.

Choice 4:

A truck motor runs for 24 hours while the truck is parked.

Here, no work is done as the force applied to run the motor is not producing any displacement (truck is parked).

So, the correct choice is first choice.

answer: the exterior temperature of commercial jet planes as they leave the stratosphere and return to the ground increases steadily.

explanation:

the lower most layer of atmosphere is troposphere which extends from 0 to 12 km above the surface of the earth. the temperature initially decreases as distance is increased from the earth's surface. commercial jets fly in lower part of the stratosphere. the stratosphere extends upto 50 km. the temperature in stratosphere starts rising again due to presence of ozone which traps the uv rays.

thus, when the planes leave the stratosphere and return to the ground, the exterior temperature increases steadily.

the answer is kevlar