by Cole07
Tags: motion, projectile, range
 P: 106 Question: How far will a stone travel over level ground if it is thrown upward at an angle of 31.0 degrees with respect to the horizontal and with a speed of 11.0m/s? What is the maximum range that could be achieved with the same initial speed? I have tried to solve this with no sucess what i have done is Drawn a triangle with a angle being 31.0 degrees the opposite side from the angle is Vy the adjacent side is Vx the hypothesis is 11.0m/s then i drew a chart with X and Y X side of the chart I have Vx= 9.428840308 a=0 then on the y side i have Vy=5.665418824 a=-9.8 the Vf=0m/s I used the formula Vf=Vi+At and solved for time and got 0.578103962 then i used d=Vi*t+1/2At^2 and solved for D and got 1.637620735 for the first question (But was told this was not correct) For the second question i doubled the time and multiplied by Vx D=9.428840308 (1.15620784) and got 10.90169909 but it was wrong ! Is there anyone who might be able to help me Please???
 P: 1,443 what is the final velocity in the Y direction? And why? for your second question how do you maximize the distance you could travel? They gave you a hint : the SPEED is thesame but something else must be different. What must change? and Why did you double time??
 P: 147 GOod grief you don't believe in rounding numbers do you???? If you've calculated, as it appears, the time taken for the vertical velocity to reach 0M/s, then you've calculated the time for the stone to reach it's maximum height, - it still has some way to go before it hits the ground. I would use here the equation x = V(i)t + 0.5 a t^2 with the vertical velocity and a = 9.8 but remembering that when the stone hits the ground its vertical displacement is zero because it started from ground level That will give you a time, then use this with the horizontal velocity (constant) to calculate the horizontal distance.
P: 106

final velocity in y direction is 0 because at the apex it is not going anywhere
 P: 147 But the apex is not the final velocity. It comes back down again.
P: 1,443
 Quote by Cole07 final velocity in y direction is 0 because at the apex it is not going anywhere
tahts fine

but is that the final velocity in the y direction for the WHOLE trip

after all you are trying to find the time it took for the ENTIRE journey
 P: 106 I get x= 1.637600545 is this right? (i am too stressed to round any numbers LOL)
P: 1,443
 Quote by Cole07 I get x= 1.637600545 is this right? (i am too stressed to round any numbers LOL)
howd you get it?
 P: 147 That's not what I got. What to you get for the time?
 P: 106 i took 5.665418824(0.578103962)+0.5(-9.8)(0.57810396)^2 and got 1.637600545
HW Helper
P: 3,224
 Quote by rsk That's not what I got. What to you get for the time?
Did you use $$y(t) = 11\cdot\sin(31)t-\frac{1}{2}gt^2=0$$ to calculate the time?

If you didn't, do so. (Solve for t.) When you do so, plug that time into $$x(t)=11\cdot\cos(31)t$$ to get the total displacement.
 P: 106 to get the time i used the formula Vf=Vi+at Vf=0m/s a= -9.8 Vi=5.665418824 (by 11.0sin(31.0)) and then i solved for time
P: 1,443
 Quote by Cole07 to get the time i used the formula Vf=Vi+at Vf=0m/s a= -9.8 Vi=5.665418824 (by 11.0sin(31.0)) and then i solved for time
why are you still saying velocity final in the Y is zero? Its NOT zero

after it has completed its entire flight what is the velocity in the Y just before it hits the ground? I certainly hope it isnt zero otherwise whatever ive been doing for these 6 odds years has been in vain! VAIN!

and this world has no justice
 P: 106 I don't understand? I am going by the example we did in class and for Vf we used 0 and this is at the apex
HW Helper
P: 3,224
 Quote by Cole07 I don't understand? I am going by the example we did in class and for Vf we used 0 and this is at the apex
Interesting class, indeed.

Btw, I suggest you do a few searches named 'projectile motion', this could do good.
 Mentor P: 4,163 That would be good to calculate the maximum HEIGHT of the object, not the maximum distance it travels. Throw a ball into the air. When it hits the ground, is the y velocity zero? Use intuition, it really helps sometimes
 P: 1,443 since im such a nice guy i drew a diagram for you look at the diagram now tell me what do u think the velocity i nteh Y direction must be after thw whole trip? THINK before you answer but dont think too hard you are probably mixing up the type of questions Attached Thumbnails
 P: 106 yes you are a nice guy but not only am i having trouble with physics BUT I CAN'T OPEN THE ATTACHMENT THIS IS SO SAD!!!!!!!!

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