Physics Question, taking general physics, week 2 questions?

First, set up a frame of reference.

That is: what is the direction of the positive x axis, and what is the direction of the positive y axis

Most commonly used is:

positive x axis to the right

positive y axis upwards

In this frame, acceleration by gravity is ALWAYS -9.8 m/s² (note the minus)

While the ball is going up (so positive velocity), the velocity will decrease because the direction of the motion is opposite to the direction of the acceleration.

While the ball is going down (so negative velocity), the velocity will increase because the direction of the motion is the same as the direction of the acceleration.

At the highest point, the velocity is momentary zero, but the acceleration is still that same acceleration by gravity.

Do you know "Newton's second law" ?

F = m × a

(force exerted on an object) = (mass of the object) × (acceleration of the object)

Now, once an object is thrown (no more contact with your hand), the only force acting on the object is the force of gravity. That force is CONSTANT. It will not change because of an object that you have thrown changes direction, or for whatever other reason.

Also, obviously the mass of the object doesn't change along its path.

So...

force of gravity is constant

mass of object is constant

which means that also

gravitational acceleration of an object must be constant, no matter at which point along its path.

You know the answers to question 1 and 2 now?

I think so ... ;-)

Now question 3...

A velocity vector is an arrow, having a certain length, and a certain direction.

The length of the arrow indicates the magnitude of the velocity.

The longer the arrow is, the bigger the SPEED of the object is.

A 'special case' is when the speed is zero. In that case the length of the arrow should also be zero, which is rather difficult to draw ... ;-)

The direction of the arrow indicates the direction of the motion.

In the frame of reference I suggested in the beginning of this answer, an upward velocity must be represented by an arrow pointing upwards, and vise verse.

If you had chosen the positive y axis to be downwards, then an upward velocity should be represented by an arrow pointing downwards.

And of course, the same for movement along the x axis.

If the positive x axis was chosen to the right, then movement to the right must be represented by an arrow pointing to the right.

If the positive x axis was chosen to the left, then movement to the right must be represented by an arrow pointing to the left.

And everything vise verse...

Again using the frame of reference I suggested in the beginning of this answer

and

for an object thrown from left to right, the direction of the arrow should be:

* before highest point: north-east

* at highest point: straight east

* after highest point: south-east

Hope this makes sense to you ...

If not; feel free to contact me ;-)

1. Answer: C. Is constant

Reason: The acceleration is gravitational acceleration, which for all practical purposes is constant near the Earth's surface. (The vertical component of the velocity is zero at the highest point.)

For 2 and 3, we assume that points ABC correspond to points PQR, respectively, in the figure

2. Answer: B. aA=aB=aC (Note Correction)

Reason: The acceleration is gravitational acceleration, which for all practical purposes is constant near the Earth's surface. (The magnitudes of the velocities at P and Q are equal)

3. Answer: d. an arrow pointed down to the right (south east)

Reason: The velocity is tangent to the curve of the trajectory