Answer:
<em>The second ball has four times as much kinetic energy as the first ball.</em>
Explanation:
<u>Kinetic Energy
</u>
Is the type of energy an object has due to its state of motion. It's proportional to the square of the speed.
The equation for the kinetic energy is:

Where:
m = mass of the object
v = speed at which the object moves
The kinetic energy is expressed in Joules (J)
Two tennis balls have the same mass m and are served at speeds v1=30 m/s and v2=60 m/s.
The kinetic energy of the first ball is:



The kinetic energy of the second ball is:



Being m the same for both balls, the second ball has more kinetic energy than the first ball.
To find out how much, we find the ratio:

Simplifying:

The second ball has four times as much kinetic energy as the first ball.
Answer: 37.981 m/s
Explanation:
This situation is related to projectile motion or parabolic motion, in which the travel of the ball has two components: <u>x-component</u> and <u>y-component.</u> Being their main equations as follows:
<u>x-component:
</u>
(1)
Where:
is the point where the ball strikes ground horizontally
is the ball's initial speed
because we are told the ball is thrown horizontally
is the time since the ball is thrown until it hits the ground
<u>y-component:
</u>
(2)
Where:
is the initial height of the ball
is the final height of the ball (when it finally hits the ground)
is the acceleration due gravity
Knowing this, let's start by finding
from (2):
<u></u>
(3)
(4)
(5)
(6)
Then, we have to substitute (6) in (1):
(7)
And find
:
(8)
(9)
(10)
On the other hand, since we are dealing with constant acceleration (due gravity) we can use the following equation to find the value of the ball's final velocity
:
(11)
(12)
(13) This is the ball's final velocity, and the negative sign indicates its direction is downwards.
However, we were asked to find the <u>ball's final speed</u>, which is the module of the ball's final vleocity vector. This module is always positive, hence the speed of the ball just before it strikes the ground is 37.981 m/s (positive).
Answer:
1.11 m/s
Explanation:
The motion of the boat is an example of accelerated motion, since the velocity is not constant. However, we don't need to find the acceleration, because we are only interested in the average velocity of the boat, which is given by:

where d is the total distance covered and t the time taken. In this problem, the boat covered a distance of d = 20 m and it takes t = 18 s, therefore the average velocity is

Answer:

Explanation:
<u>Elastic Potential Energy
</u>
Is the energy stored in an elastic material like a spring of constant k, in which case the energy is proportional to the square of the change of length Δx and the constant k.

Given a rubber band of a spring constant of k=5700 N/m that is holding potential energy of PE=8600 J, it's required to find the change of length under these conditions.
Solving for Δx:

Substituting:

Calculating:


Answer:
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