Excel HSC ques (1 Viewer)

[pc_wizz]

"In Newton's imaginary analysis of projectile motion, a cannon was used to fire a cannon ball horizontally from the top of a high mountain. Which one of the graphs in Figure 1.31 best represents the horizontal velocity of the cannon ball against time if we neglect air resistance?"

this is from Excel HSC Physics Space Test ... q5 ...

four graphs are shown, they are all velocity-time graphs ...

i chose the one that was constant velocity ... however the book gave it a wrong answer ... it put the right answer as the one with a sloped straight line that looks like the graph of y=x ... now isnt horizontal velocity constant? ...

 

[Tommy_Lamp]

the fact that they said "neglect air resistance" means that they are hinting that, so i would say that you have the right answer and the book has made a mistake

 

[Xayma]

Well strictly speaking horizontal velocity (parallel to the original plane) is accelerating, as you must take into account gravity and the curvature of the earth at a high mountain, as hinted by Newton's imaginary analysis of projectile motion.

 

[Tommy_Lamp]

i always thought that horizontal velocity was constant?!

 

[chazza]

Well strictly speaking horizontal velocity (parallel to the original plane) is accelerating, as you must take into account gravity and the curvature of the earth at a high mountain, as hinted by Newton's imaginary analysis of projectile motion.

err...how can the horiztonal velocity be accelerating,if there is no air resistance?

With no air resistance.. the horiztonal velocity should be contant

and gravity is only taken into account in the vertical veolcity

so what you saying Xayma doesnt really make sense....

please explain.. how you got that??

 

[Tommy_Lamp]

thats what i thought chazza, the only natural force acting on the horiontal velocity is air resistance, and since there isnt any......

 

[*Pooja*]

dammit! im going to get it right this time now... horizontal motion is constant velocity (zero acceleration when neglecting air resistance), and vertical velocity is uniformly accelerated motion. they r both totally independent of each other.

pc_wizz: i know the exact question ure talking about coz my whole class started pissing the teacher off with that question. the answer is (a) - the straight line one. so its a printo.

 

[pc_wizz]

thanx for that reassurance ... appreaciate it

 

[Xayma]

But Newton's idea of firing a cannon was that eventually you could send it into orbit if the tower was high enough, because of the curvature of the Earth.

Not everything has to do with nice flat surfaces, the earth is curved when it goes 90 degrees it will be the only thing accelerating.