Conceptuals:

16) A rocket becomes progressively easier to accelerate as it travels through space. Why is this so? (hint - about 90% of the mass of a newly launched rocket is fuel).

21) For each of the following forces, what is the equal and opposite force required by Newton's 3rd law?
a, the force of a hammer on a nail;
b, the force of gravity pulling down on a book;
c, the force of a helicopter blade pushing down on the air; or
d, the force of air resistance acting on a thrown baseball.

35) As the speed of an object moving through a fluid increases, what happens to the friction acting on it? As the area of the object increases, what happens to the fluid friction?
A: If the speed of the object moving through a fluid increases, the friction acting on it should increase (to balance the net force), but if the area increases (while the speed remains the same), the friction should remain the same.

Question

Conceptuals:

16) A rocket becomes progressively easier to accelerate as it travels through space. Why is this so? (hint - about 90% of the mass of a newly launched rocket is fuel).

21) For each of the following forces, what is the equal and opposite force required by Newton's 3rd law?
a, the force of a hammer on a nail;
b, the force of gravity pulling down on a book;
c, the force of a helicopter blade pushing down on the air; or
d, the force of air resistance acting on a thrown baseball.

35) As the speed of an object moving through a fluid increases, what happens to the friction acting on it? As the area of the object increases, what happens to the fluid friction?
A: If the speed of the object moving through a fluid increases, the friction acting on it should increase (to balance the net force), but if the area increases (while the speed remains the same), the friction should remain the same.

kittiwitti1 · Answer

@AllTehMaffs @Mashy

anonymous · Answer

16) Fuel is used up, decreasing mass. As a = F/m, as m decreases, less force is needed to get the same acceleration, resulting in 'easier' acceleration.

kittiwitti1 · Answer

Ok gotcha

anonymous · Answer

21) a) A normal force (Nail pushes back up onto the hammer)
b) Gravity 'pulls' the earth in the opposite direction
c) Air 'pushes' back on the blade (lift)
d) The ball 'pushes' air out of the way

kittiwitti1 · Answer

Alright, thanks @PhoenixW! (:
If it's okay with you could you check my answer for the last question? ^-^

anonymous · Answer

" the friction acting on it should increase (to balance the net force)" ? this makes absolutely no sense.. u are right though that drag force (its so horrible to call it as friction) increases.. but the reason it does. has something to do with viscosity and other concepts of fluid mechanics which can get really complicated. so what exactly are u learning there in that chapter?

"but if the area increases (while the speed remains the same), the friction should remain the same"

imagine taking a  paper ball .. and letting it drop, and imagine making that same paper flat and dropping.. considering air drag.. which one falls first? that should answer ur second question!

kittiwitti1 · Answer

Okeydoke thanks @Mashy (;