Thread: My physic questions.

Originally Posted by BlackDeath

Elkvis thank you. Answer is Acceleration is constant . WHY ANSWER ACCELERATION IS CONSTANT ?

2) Which one of the following is wrong for the motion with constant velocity?
A) Acceleration is constant

An object with constant velocity has zero acceleration, which is technically constant. However, constant acceleration does not automatically imply zero acceleration, so this is the best answer, even though it's still a bad option.

B)Average velocity is constant
C) Instantaneous velocity is constant

These are both true of objects with constant velocity. An object with constant velocity will have constant average and instantaneous velocity.

D)Acceleration is 0

An object with constant velocity is, by definition, not accelerating, so this is also true of an object with constant velocity.

Originally Posted by Elkvis

An object with constant velocity has zero acceleration, which is technically constant.

Careful. In physics, 0 acceleration is the absence of acceleration. No acceleration.

Originally Posted by Elkvis

this is the best answer, even though it's still a bad option.

This is the best answer and is a good option, for the reason above. i.e. A constant acceleration implies the existence of an acceleration. But 0 acceleration means no acceleration. An object with 0 acceleration is moving (or is stationary) with no acceleration at all.

So this answer is technically the right answer.

Originally Posted by Mario F.

Careful. In physics, 0 acceleration is the absence of acceleration. No acceleration.

But zero isn't a magic number with special meaning, even with acceleration. Constant zero is still constant. The property doesn't cease to exist, simply because its value is zero.

Originally Posted by Elkvis

But zero isn't a magic number with special meaning, even with acceleration. Constant zero is still constant. The property doesn't cease to exist, simply because its value is zero.

Don't confuse the mathematical zero with the informal 0 in an informal conversation. The mathematical zero is a constant, or to be more precise, a mathematical literal. But in physics there is no 0 acceleration. That is simply an informal, and in fact quite imprecise, expression.

Remember, acceleration is represented mathematically not as a literal (or constant if you will), but as a vector. A zero vector (or null vector) is a vector with 0 magnitude and no direction. A null vector represents no acceleration, not the literal 0.