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Ok, acceleration is the rate of change of velocity.

So if the velocity of one object changes, this means that the object is accelerating.

Also, remember that velocity is a vector, this means that has a direction, then if for example the direction of motion changes slightly we have acceleration.

A) The correct option is D, all the choices given are correct. (by definition of acceleration)

B)

If you have positive velocity, negative acceleration means that your velocity will decrease.

While if you have a negative velocity, negative acceleration will decrease your velocity, making it bigger in module, thus increasing your speed.

Then we can not say anything conclusive of what happens only knowing the sign of the acceleration.

Then the correct option is the trivial one "the object moves on a straight line". option D

C) Any unit that is the quotient between a distance unit and a squared time unit.

for example: m/s^2,  km/s^2, etc.

Here the correct option is A.

"meters per squared second" is equal to m/s^2

D) If you steep inside the carrousel you will not move in a straight line, this means that while your speed is constant, it is changing direction constantly, then you are accelerating.

The correct option is D.

C) Both motorcycles A and B are changing their speeds, while motorcycle C is changing its direction, then the 3 are accelerating.

The correct option is D

E) Assuming that the velocity of the jeepney is positive, if the jeepney speeds up, then it must have positive acceleration, then the correct option is: B

the ratio of balloons to tables is 5: 2 and the constant variation is 5.

the equation is y=5x

can you complete your sentence? i could !