another physics doubts

[helllife]

question is.......

On a foggy day, two car drivers spot each other, when they are just 80m apart. They are travelling at 72km/h and 60km/h respectively. Both of them simultaneously apply breaks when retard the cars at 5m/s². Determine whether they avert the collision or not?

what would the answer and can u please show the working of how u got the answer?

[vaan]

question is.......

On a foggy day, two car drivers spot each other, when they are just 80m apart. They are travelling at 72km/h and 60km/h respectively. Both of them simultaneously apply breaks when retard the cars at 5m/s². Determine whether they avert the collision or not?

what would the answer and can u please show the working of how u got the answer?

when de break is applied...de 1st car....it takes goes...72/5 = 14.4m
for de second car....after breaks r applied it moves...60/5 = 12m
dey already have a distance of 80m...n even after de breaks r applied de distance increases 14.2 - 12 = 2.2m
so de total distance between cars now is 80 + 2.4 = 82.4m...
hence dey don have a crush.....

[helllife]

do u mean (70/5) as (a/v)? isnt it time?? how did u find in distance?

[astarmathsandphysics]

72km/h=72000/3600=20m/s
and 60km/h=16.67m/s

v^2=u^+2as for each car
0=20^2+2*-5*s so s=40m for car 1
0=16.67^+2*-5*s so s=27.78 for car 2. The cars close by 67.78 so do not collide.

[helllife]

thanks astar!!! 
i have another question....on projectile.....

A fighter plane flying horizontally at an altitude of 1.5km with a speed of 720km/h passes directly overhead an anti-aircraft gun. At what angle from the vertical should the gun be fired for the shell with muzzle speed 60m/s to hit the plane?

the answe is 19.47', can u show the workings??

[astarmathsandphysics]

Will when i get home.

[helllife]

Will when i get home.

okay, no problem, take your time!!

[astarmathsandphysics]

I post to questions like this to make it easy to find the post when i get home.

[astarmathsandphysics]

A fighter plane flying horizontally at an altitude of 1.5km with a speed of 720km/h passes directly overhead an anti-aircraft gun. At what angle from the vertical should the gun be fired for the shell with muzzle speed 60m/s to hit the plane?

the answe is 19.47', can u show the workings??
Coordinate of plane are(200t,1500)
coordinates of shell are (60tsinx, 60tcosx-0.5*9.8t^2)
hence
1500=60tcosx-0.5*9.8t^2 (1)
200t=60tsinx (2)

Are you sure the speed of the shell is 60m/s? It will never catch the plane?

I think it is 600
if it is then (2) becomes 200t=600tsinx so sinx=1/3 so x=sin^-1(1/3)=19.47 degrees

[helllife]

thank you...... i understood.......i think the speed should be 600m/s...

so basically, we are using pythorus theorum...right?
 
can use write in this way,
cosx = 200/600
x=70.52
to find the angle from vertical......
y= 90-70.52
  = 19.48?