Explanation:
- Newton's first law of motion:
"An object at rest (or in uniform motion) remains at rest (or in uniform motion) unless acted upon an unbalanced force
In this situation, we can apply Newton's first law to the keys of the keyboard that are not hit by the fingers of the man. In fact, as no force act on the keys, they remain at rest.
- Newton's second law of motion:
"The acceleration experienced by an object is proportional to the net force exerted on the object; mathematically:

where F is the net force, m is the mass of the object, and a its acceleration"
In this case, we can apply Newton's second law to the keys of the keyboard that are hit by the man: in fact, as they are hit, they experience a downward force, and therefore they experience a downward acceleration.
"Newton's third law of motion:
"When an object A exerts a force on an object B (action force), then object B exerts an equal and opposite force on object A (reaction force)"
Here We can apply Newton's third law to the pair of objects finger-key: in fact, as the finger apply a force on the key (action force), then the key exerts a force back on the finger (reaction force), equal and opposite.
Answer:
Milimeters
Explanation:
This kind of question must be checked with everyday elements, in this way we will analyze each of the options until we reach the appropriate:
kilograms can not be because this unit serves to measure the mass not the length.
kilometers (km) is a unit of length, but however it does not serve for this measurement since a km is equivalent to 1000 meters, therefore measuring the length of a shoe with a ruler measuring 1000 meters is very impractical.
milliliters is a unit of volume, and can often be found in the measurement of volume content of liquids, for example 700 milliliters of milk or 1000 milliliters of water. Therefore it is impractical to measure a shoe with a unit of volume.
In this way the way to measure a shoe correctly is using a ruler or measuring instrument graduated in millimeters.
the answer to your question would be D.
Not sure if this it completely right but here’s what I got: 77.16050617284 J