James Bond Mission: Find Height of Cannon from Sea

[maxtheminawes]

Homework Statement

James Bond job is to aim at clifftop cannons at attacking vessels coming from the sea. In one practice exercise he shoots her cannon at an angle of 40 degrees, giving the cannon ball a velocity of 35m/s. If the cannon ball lands 150m from the base of the cliff, how high is James abouve the sea.

Homework Equations

v=vo+at
y=yo+vot+1/2at^2
y=height

The Attempt at a Solution

v=vo+at
35=(-9.8)t
t=3.57secs

y=yo+vot+1/2at^2
y=35sin40(3.57)+1/2(-9.8)3.58^2
y=17.87m

 

[TaxOnFear]

Are you familiar with projectile motion? Try splitting the attack into two parts, where the cannon ball is rising (-ve g) and where it falls (+ve g). Resolving your velocity into components will give you a good start.

 

[LawrenceC]

Alternately, since the horizontal velocity of the cannon ball is constant in time (no air drag), you can compute the time of flight of the shot. Knowing that and the initial vertical velocity component, you can compute the vertical distance by using the projectile motion equation for y. Just be careful with the signs in the equation.

 

[maxtheminawes]

ok, i retried the problem. is this right?
x=vt
150=35cos40t
t=5.59 sec

y=Voyt+1/2at^2
y=35sin40(5.59)+1/2(-9.8)(5.59^2)
y=27.35m

 

[LawrenceC]

ok, i retried the problem. is this right?
x=vt
150=35cos40t
t=5.59 sec

y=Voyt+1/2at^2
y=35sin40(5.59)+1/2(-9.8)(5.59^2)
y=27.35m

That's it essentially but you have a sign error. y = -27.35 based on your equation.