How Long Before Hearing a Sonic Boom from a Supersonic Plane at Mach 3?

[ScienceGeek24]

Homework Statement

A supersonic plane flies at Mach 3 at an altitude of 20,000 m. A person on the ground sees the plane directly overhead. How much time passes the before she hears the sonic boom?

Homework Equations

f=fo(v+-vo/v-+vs)

The Attempt at a Solution

I don't really know how to start up with this one, I was hoping for some help here.

 

[PeterO]

Homework Statement

A supersonic plane flies at Mach 3 at an altitude of 20,000 m. A person on the ground sees the plane directly overhead. How much time passes the before she hears the sonic boom?

Homework Equations

f=fo(v+-vo/v-+vs)

The Attempt at a Solution

I don't really know how to start up with this one, I was hoping for some help here.

The sonic boom is just a noise produced by the plane, which has to travel 20,000m to reach you.
The answer would be the same if it was a helicopter hovering at 20000m then firing a really loud gun - or with a really big sound system playing AC-DC.

 

[ScienceGeek24]

So what equation do you suggest I can use to start up the problem?

 

[PeterO]

So what equation do you suggest I can use to start up the problem?

You want to calculate the time taken for sound to travel 20000m. What equation do you think you need - it connects speed, time and distance?

You will need to know the speed of sound - and will probably have to make the assumption that it remains constant all the way from up there to down where you are!