# Zero net force acting on it

1. Sep 9, 2009

### DUCEDAWG

Which of the following describes an object with zero net force acting on it? Choose all that apply.

A car sped along at a constant rate while making a left turn.
A truck sped up while proceeding along a straight path.
A plane slowed down while making a u-turn.
A boat accelerated at a constant rate while making a right turn.
A rocket moved at a constant speed while moving in a straight line.

I know that zero net force means that it has no acceleration, Sped up means accelerating. I picked the 1st and last one it was wrong.

2. Sep 9, 2009

### fatra2

Hi there,

You are right by saying that an object that accelerates is necessarily submitted to external forces. Can you tell me what is the acceleration is your last example???

Cheers

3. Sep 9, 2009

### DUCEDAWG

There isn't any acceleration acting on the rocket.

4. Sep 9, 2009

### CompuChip

Hint: acceleration is not just a number. ;)

5. Sep 9, 2009

### DUCEDAWG

CompuChip, I truly don't understand. What do you mean acceleration is not just a number?

6. Sep 9, 2009

7. Sep 9, 2009

### DUCEDAWG

So, therefore, the answer is A rocket moved at a constant speed while moving in a straight line

8. Sep 9, 2009

### Chewy0087

correcto, but are you sure you understand WHY? this is a really key key thing in understanding acceleration, velocity and vectors in general