Answer: D
Explanation:
Let us examine the given actions to see which ones generate heat and sound energy from mechanical energy.
A) Stretching a string.
The mechanical stretching creates tension in the string, which is released when the tension is removed. The generation of thermal or sound energy is minimal or negligible.
B) Squeezing a sponge ball
The sponge ball experiences compressive loading. This generates minimal or no heat and sound energy.
C) Throwing a ball upwards in the air
Air friction generates minimal or no heat at low velocities. At low velocities the pressure waves are too small to generate sound.
D) Striking a hammer on a nail.
A tremendous amount of force is applied over a small area to generate very high stresses that are in the plastic zone. A high amount of thermal energy is generated and the localized disturbance of the air generates audible sound.
This is the correct situation.
Answer:
Explanation:
The initial mechanical energy of the object, when it is located at height h above the the planet, is just gravitational potential energy:
where
G is the gravitational constant
M is the mass of the planet
m is the mass of the object
R is the radius of the planet
h is the altitude of the object
When the object hits the ground, its mechanical energy will sum of potential energy and kinetic energy:
where
v is the speed of the object at the ground
Since the mechanical energy is conserved, we can write
and solving for v, we find
Answer:
In order to move forward, Letti needs to be creative.
Explanation:
Creative:
A person is said to be creative if that person has ability to think out of the box.
For example: if a person having a problem and instead of using traditional methods of solving the problem then that person thinks about news ideas then that person is creative,
As in our case, letti can use problem solving technique to find a solution of her problem.
Creative Problem technique:
It is such a problem solving method in which we use unconventional ways to get the solution of a problem. We analyze the problems with news view points so that we can reach at innovative ideas of solutions.
Answer:
The bicycle slows down because of the frictional force acting on the tyres of the bicycle. When this frictional force overcomes the force applied by paddling, the bicycle stops.
