# Some physics questions

#### allstar1

The answers that i think are correct have ***** next to them. If anyone knows the right answers please share your thoughts. Thank you.

1. A ball is thrown downward (not dropped) from the top of a tower. After being released, its downward acceleration will be
Choices:
greater than g.
exactly g. *****
less than g.
none of the above

2. A rock is thrown up at a 45° angle. Neglecting air resistance, the x-component of the rock's velocity is
Choices:
greatest just after the rock is thrown
greatest at the top of the rock's flight
greatest just before the rock hits the ground
always the same *****

3. Velocity measurements
Choices:
differ in defferent frames of reference. *****
are the same in any Galilean reference frame.
are always largest in the reference frame of the Earth.
are always smallest in the reference frame of the Earth.

4. Which of these laws is not one of Newton's laws?
Choices:
Action force equals reaction force
F = ma
All objects fall with equal acceleration *****
Objects at rests stay at rest, etc.

5. Inertia
Choices:
expresses the tendency of bodies to maintain their state of motion. *****
is Newton's third law.
none of the above

6. If vector B is added to vector A, the resultant vector A+B has a magnitude A+B when A and B are
Choices:
perpendicular to each other
oriented in the same direction *****
oriented in opposite directions
in any direction relative to each other

Thank you.

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#### zwtipp05

I believe the only one you missed is #1. What is your reasoning for your choice? Think about it. When you throw a ball upward is there a change in velocity? What happens when you throw it down?

#### allstar1

zwtipp05 said:
I believe the only one you missed is #1. What is your reasoning for your choice? Think about it. When you throw a ball upward is there a change in velocity? What happens when you throw it down?
Acceleration is only at a constant 9.8m/s2 in free fall only. So considering there is air resistance i guess that Acceleration has to be less than 9.8 m/s2 then. LMK

#### HallsofIvy

Homework Helper
That argument I would accept. But you originally marked "none of the above"! Surely any acceleration must be "equal to g" OR "less than g" OR "larger than g"!

#### allstar1

how can acceleration be "larger than g"???

#### allstar1

HallsofIvy said:
That argument I would accept. But you originally marked "none of the above"! Surely any acceleration must be "equal to g" OR "less than g" OR "larger than g"!
so what would you say is the best answer from "equal to g" OR "less than g" OR "larger than g". I really don't think acceleration would be "larger than g" unless there is some kind of a trick to this question, but not really sure about the other 2 choices.

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#### Neohaven

G is the acceleration due to gravity? if yes, i think you could say that higher than G is possible... dont rely only on me, but id say that an object thrown downward has initial acceleration due to the hand which could be greater than G...

#### Doc Al

Mentor
The question is asking about the acceleration after being released, so any extra acceleration due to the force of the hand is irrelevant. The only ambiguity is whether to consider air resistance or not. Ignoring air resistance, the acceleration is exactly g. Air resistance reduces the acceleration (consider the net force on the object), since the object is thrown downward.

(Halls' point was that the first three choices cover all the possibilities! )

#### Neohaven

Doc Al said:
The question is asking about the acceleration after being released, so any extra acceleration due to the force of the hand is irrelevant. The only ambiguity is whether to consider air resistance or not. Ignoring air resistance, the acceleration is exactly g. Air resistance reduces the acceleration (consider the net force on the object), since the object is thrown downward.
Thanks! I'll know it from now on

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