i think is is an incorrect test question?

[BoneMental]

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The question is:

Given the initial velocity, which of the following is the least amount of info that could be used to determine how far a projectile lands from a cannon?
A) time to travel, angle of elevation
B) acceleration of gravity
C) angle of elevation, acceleration of gravity
D) height of the peak of the projectile

The correct answer is B, but I said C.

The explanation given for why B is correct is that you can break the system down into X and Y components. However, how can you do this if you don't know the angle of elevation? You don't know the x-velocity or the y-velocity...

What do ya'll think?

 

[MT Headed]

You are thinking speed, which is a scalar. This question says they gave you velocity, which is a vector. If you know initial velocity, you know both the initial speed and the initial direction of the projectile.

This is a wordplay type question that is hounded upon repeatedly in chapter 1 of exam krackers physics. I've never seen something like this tested on an actual mcat question, but EK physics will make you absolutely b@t**** paranoid about questions like these. In fact, I immediately though to myself "is the ground flat? is there any air resistance?".

 

[BoneMental]

You are thinking speed, which is a scalar. This question says they gave you velocity, which is a vector. If you know initial velocity, you know both the initial speed and the initial direction of the projectile.

This is a wordplay type question that is hounded upon repeatedly in chapter 1 of exam krackers physics. I've never seen something like this tested on an actual mcat question, but EK physics will make you absolutely b@t**** paranoid about questions like these. In fact, I immediately though to myself "is the ground flat? is there any air resistance?".

No, I wasn't thinking that :/

If you know the initial velocity, you know the direction and the magnitude. That does NOT mean you know the components, nor does it mean you know the angle the projectile was launched.

For example, if you know the initial velocity is 30m/s at an angle theta to the horizontal, how could you solve the problem if you don't know theta? There's no way to know the components is there?

 

[aln012]

I think thats what MT headed was talking about when he said wordplay. Knowing the "velocity" implies that you know the magnitude AND the angle of elevation. If you just know 30m/s at an angle theta, then that means you don't fully "know" the velocity.

 

[Isoprop]

No, I wasn't thinking that :/

If you know the initial velocity, you know the direction and the magnitude. That does NOT mean you know the components, nor does it mean you know the angle the projectile was launched.

For example, if you know the initial velocity is 30m/s at an angle theta to the horizontal, how could you solve the problem if you don't know theta? There's no way to know the components is there?

The other posters are absolutely right. If you know the initial velocity is 30 m/s and not know the angle, then you don't really know the velocity, you just know the speed.

Knowing the velocity means you know the speed and the direction. That means you know the x and y components or angle or some other notation to show direction (like saying north by northeast).

 

[BoneMental]

Ohhhhh, I thought it just meant like a general direction. Well that's good to know! Thank you everyone