Projectile Motion Problem

[aznboy50]

Ahh shit, I remember now, give me a sec It can be done.

Please do it!!!!!!!

I've been trying to solve this for over half an hour!!!

[bomb]

Which textbook is it from aznboy? If heinemann, which question?

[aznboy50]

It's not from a textbook apparently...

I mean this question :

A car has run into a fire hydrant and come to an abrupt stop. A suitcase tied to a rack on top of the car has been thrown off and landed on the roadside 11.6m away from the hydrant. The suitcase is found to have been 1.2m above the ground when it was still on the rack. Determine the impact speed of the car if the launching angle for the suitcase was 10degrees.


I'm telling you now, you can't solve it.

[bomb]

I know which question you meant, just wanted to see if it's the same one I did a while go. I remember doing a similar one. I do think there's information missing...

Edit, found the question I did, it was very similar BUT it had the time at max height.

[aznboy50]

I know which question you meant, just wanted to see if it's the same one I did a while go. I remember doing a similar one. I do think there's information missing...

Edit, found the question I did, it was very similar BUT it had the time at max height.

That explains it...

[laijiawen]

Here's the picture, I'll try and latex and answer in a sec First time latexing, bear with me.

Time taken for the suitcase to hit the ground:











So, lets find the velocity




Someone that's actually good at physics please check this. I suck at physics, but wanted to help

The answer says 14.5m/s. I think you forgot to take into account the angle and stuff. This question stumps me ~.~. Plus it has a Challenging written next to it by the teacher.

[kamil9876]

You definitely don't need the mass. It's solvable using just kinematics.

edit: just two points:

(1) your teacher didn't mention whether the angle is up or down.
(2) doesn't seem very realistic that there should be a "launching angle" since by newton's (first?) law it seems as though there would need to be some force applied at such an angle in order to change the direction of the suitcase.

But with some (possibly bullshit) assumptions, it is solvable with just kinematics.

[s2penguin]

You definitely don't need the mass. It's solvable using just kinematics.

Could you please do it, I too cannot do it?

[evaever]

vertical: u=vtan10, a=-10, s=-1.2, t?   s=ut+0.5at2

horizontal: u=v, s=11.6, t?   s=ut

eliminate t to find v=14.5

[s2penguin]

How did you get the initial vertical velocity u= vtan10?

[evaever]

(1) your teacher didn't mention whether the angle is up or down.
It has to be up, otherwise it goes through the roof of the car.
 
(2) doesn't seem very realistic that there should be a "launching angle" since by newton's (first?) law it seems as though there would need to be some force applied at such an angle in order to change the direction of the suitcase.
It is realistic because when the car hits the obstacle the rear may tilt upwards and project the suitcase at an angle, keep in mind the car is not a point.

[kamil9876]

Yeah just thought about it before and realised the car could also be going up a ramp, still it could be going down a ramp(or the road could be tilted a bit down). But anyway what is certain is that you can calculate the initial speed of the suitcase without any ambiguity.

[evaever]

you are number 1

when a horizontal jet of water hits a wall, water goes in all directions after reflection, not just horizontally

[laijiawen]

vertical: u=vtan10, a=-10, s=-1.2, t?   s=ut+0.5at2

horizontal: u=v, s=11.6, t?   s=ut

eliminate t to find v=14.5

so is this the answer?

[bomb]

No, because like me ha has put distance as 1.2m, when the suitcase goes up first...