# Homework Help: Projectile Motion maximum height

1. Dec 3, 2007

### salman213

1. http://img525.imageshack.us/img525/6376/fic11p112xe1.png [Broken]
http://img525.imageshack.us/img525/9550/vqc11p112el8.png [Broken]
[/URL]

2. d = 1/2at^2 + v1t

v =d/t

3.
horizontal time it takes equals vertical time

Horizontal
t = d/v = 50 /(v1cos10)

Vertical
d = 1/2at^2 + v1t
-0.6 = 1/2(-9.81)(50/v1cos10)^2 + v1sin10(50 /(v1cos10)

i get v1 = 36.6 m/s

-1.6 = 1/2(-9.81)(50/v1cos10)^2 + v1sin10(50 /(v1cos10)
i get v1 = 34.8 m/s

So my range is 34.8 m/s to 36.6 m/s

for b part

dv = v1(t) - 1/2(9.81)(t^2)

maximum height occurs at half the time so i used 1/2(50/v1cos10)

dv = 34.8(1/2(50/36.64cos10) - 1/2(9.81)(1/2(50/34.8cos10))^2
i got 22.8 m

for 2nd velocity

dv = 36.64(1/2(50/36.64cos10) - 1/2(9.81)(1/2(50/36.64cos10))^2
i got 23.0 m

So my maximum height range is 22.8 m to 23.0 m

According to my online assignment this is wrong

plz helppppppppppp

Last edited by a moderator: May 3, 2017
2. Dec 3, 2007

### salman213

ALSO:

i just noticed for maximum height i guess I also add 2.1 m if they are measuring from the Ground so 22.8 + 2.1 = 24.9 m and 23.0 + 2.1 = 25.1 m but these values still are somehow wrong........

3. Dec 3, 2007

### salman213

i know it may be a little long in calculating but can someone check to see if my process is right if no one wnats to check my calculations :)

4. Dec 3, 2007

### Vipul

Hi Salman, i have been doing some work on this problem, Would you please be so kind to include the correct answers so i can verify and post it?

5. Dec 4, 2007

### salman213

if i had the correct answers i wouldnt have posted it :(

wat answers did u get? and how did u attempt this problem differently?

Thanks..

6. Dec 4, 2007

### salman213

vipul did u get different answerS?

7. Dec 4, 2007

### Vipul

sorry salman, havent got the answers yet but still working on them, i thought if u had the correct answers, maybe we can work backwards.

8. Dec 5, 2007

### salman213

hmm ok if u get answers tell me because i can keep submitting the answers repeatedly on my assignemtnt o see if they are right but I need the right answer. I dont understand what Im doing WRONG!!!!!!!!!!!!!!!

also do u have a energy question? about a spring and stuff? Did u fnish that one :S?

9. Dec 5, 2007

### Vipul

Salman, for part (a), my answers; the range is between 34.99m/s to 36.82m/s. Could you please verify these?

10. Dec 6, 2007

### salman213

hmm its one question so try getting b part too about maximum height range,

like its ONE question

a)
b)

and u have to enter both answers.

then i can cehck if they are right,

if someone else can check my solution plz do, i dont know where im going wrong!

11. Dec 8, 2007

### Vipul

a) 34.99m/s to 36.82m/s
b) 3.99m to 4.18m

12. Dec 8, 2007

### salman213

lol its too late sry my assignments done

13. Dec 8, 2007

### Vipul

Did u get the correct answers?