1) The grapefruit is in free fall, so it moves by uniformly accelerated motion, with constant acceleration

. Calling h its height at t=0, the height at time t is given by

We are told thatn when

the grapefruit hits the ground, so h(0.75 s)=0. If we substitute these data into the equation, we can find the initial height h of the grapefruit:


2) The speed of the grapefruit at time t is given by

where

is the initial speed of the grapefruit. Substituting t=0.75 s, we find the speed when the grapefruit hits the ground:
If the 5,500 J of sound and light is the ONLY useful output
from the phone, then the phone's efficiency is
(5,500J / 10,000J) = 0.55 = 55% .
But the test engineer forgot one little minor almost insignificant detail.
As a test engineer myself, I'd say that he needs to turn in his laptop
and soldering iron, and think about changing his career to a job for
which he may be better suited, like 8 hours a day in a highway toll-booth.
What about that little radio transmitter and receiver inside the phone,
that maintain digital RF communication with the nearest cell tower ?
Without that microscopic radio transceiver ... plus 30 or 40 apps
that are always running unless you shut them off ... the device in your
pocket is essentially a flat rock with one side that sometimes glows.
Answer:
W = 0 J
Explanation:
It is given that,
Weight of the crate, W = 100 N
Distance moved by the crate, d = 1.5 m
Let W is the work done to hold the crate 1.5 m above the ground in this way. It is given by the product of force and the displacement. Its formula is given by :

Here,
as it is lifted vertically
W = 0
So, the work done to hold the crate is 0. Hence, this is the required solution.