Answer:
The length of her shadow is changing at the rate -2 m/s
Explanation:
Let the height oh the street light, h = 22 ft
Let the height of the woman, w = 5.5 ft
Horizontal distance to the street light = l
length of shadow = x
h/w = (l + x)/x
22/5.5 = (l + x)/x
4x = l + x
3x = l
x = 1/3 l
taking the derivative with respect to t of both sides
dx/dt = 1/3 dl/dt
dl/dt = -6 ft/sec ( since the woman is walking towards the street light, the value of l is decreasing with time)
dx/dt = 1/3 * (-6)
dx/dt = -2 m/s
The initial height of the first body is given by:
where
g is the gravitational acceleration
t is the time it takes for the body to reach the ground
Substituting t=1 s, we find
The second body takes takes t=2 s to reach the ground, so it was located at an initial height of
The second body started its fall 1 second before the first body, therefore when the second body started its fall, the first body was located at its initial height, i.e. at 4.9 m from the ground.
I can't guess what -9.8 m/s means until you tell me where it came from,
or what 'm/s' means.
If perhaps it has something to do with the acceleration of gravity on Earth,
then the correct figure is ' -9.8 m/s² '. That means that any object that
has no other force acting on it except gravity has its speed changing by
9.8 meters per second every second. Since it's gravity doing the job,
then the object's speed is either increasing down, or decreasing up.
If an object has negative velocity, then it's moving in the direction opposite
to the direction that you decided to call positive when you started doing the
problem.
For example, if you decide that up is positive and down is negative, and
then somebody drops a stone from the top of a tall building, then the
gravitational force on the stone is negative (pointing down), its velocity
is negative (it's falling towards down), and its acceleration is negative (its
speed towards down is getting faster and faster). Everything is negative,
only because you decided that up is positive and down is negative. It's
nothing to be worried about.
B is the correct answer.
A is incorrect because energy is neither created nor destroyed.
C is incorrect because kinetic energy would keep the ball rolling, so that would not make sense.
Answer:
Newtons law of conservation energy says that energy cannot be created or destroyed because energy is always made into something else. It is always reused.
Explanation:
