Aussie NSW Year 12 Projectile Motion Question.

  • Thread starter f3nr15
  • Start date
  • #1
22
0

Homework Statement



A projectile has a time of flight 7.5s and a range 1200m
calculate
(a) its horizontal velocity
(b) Its maximum height
(c) the velocity witch which it is produced

I take ay as -9.8ms-2

Homework Equations



r = uxt
dy = uyt + (ayt2/2)
vy2 = uy2 + 2ah
ux2 + uy2 = u
v = u + at

The Attempt at a Solution



I hope I am the correct

a) r = uxt

ux = r/t
ux = 1200/7.5
ux = 160m

.: Initial Horizontal Velocity is 160m

b)

dy = uyt + (at2/2)

dy = 0 (Total vertical displacement is zero)
0 = 7.5uy - 275.625
7.5uy = 275.625
uy = 36.75

vy2 = uy2 + 2ah

vy = 0
0 = 1350.5625 - 19.6h
19.6h = 1350.5625
h = 68.90625 ...

.: Maximum height is 68.91m-1

c)

ux2 + uy2 = u

(160)2 + (36.75)2 = 26950.5625
u = 164.1662648 ...

.: Initial Velocity is 164.17ms-1

v = u + at

v = (164.1662648) + (-9.8)(7.5)
v = 90.6662648 ...

.: Final Velocity is 90.67ms-1


Ya ?
 

Answers and Replies

  • #2
PhanthomJay
Science Advisor
Homework Helper
Gold Member
7,166
507

Homework Statement



A projectile has a time of flight 7.5s and a range 1200m
calculate
(a) its horizontal velocity
(b) Its maximum height
(c) the velocity witch which it is produced

I take ay as -9.8ms-2

Homework Equations



r = uxt
dy = uyt + (ayt2/2)
vy2 = uy2 + 2ah
ux2 + uy2 = u
v = u + at

The Attempt at a Solution



I hope I am the correct

a) r = uxt

ux = r/t
ux = 1200/7.5
ux = 160m

.: Initial Horizontal Velocity is 160m

b)

dy = uyt + (at2/2)

dy = 0 (Total vertical displacement is zero)
0 = 7.5uy - 275.625
7.5uy = 275.625
uy = 36.75

vy2 = uy2 + 2ah

vy = 0
0 = 1350.5625 - 19.6h
19.6h = 1350.5625
h = 68.90625 ...

.: Maximum height is 68.91m-1

c)

ux2 + uy2 = u

(160)2 + (36.75)2 = 26950.5625
u = 164.1662648 ...

.: Initial Velocity is 164.17ms-1

v = u + at

v = (164.1662648) + (-9.8)(7.5)
v = 90.6662648 ...

.: Final Velocity is 90.67ms-1


Ya ?
a, b, and c look correct numerically, but your units generally are not. Then you added a part d which is not correct. You've got to look in the vertical and horizontal direction separately. Since energy is conserved, what might the final velocity be?
 

Related Threads on Aussie NSW Year 12 Projectile Motion Question.

Replies
4
Views
167
Replies
1
Views
10K
  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
4
Views
1K
Replies
8
Views
2K
Replies
5
Views
1K
Replies
3
Views
1K
  • Last Post
Replies
3
Views
1K
Replies
7
Views
6K
  • Last Post
Replies
2
Views
8K
Top