Year 10 Physics Question

Im not sure how to do this question so can you please please show all of your steps? Thanks so much

A airplane has a lift off of 120km/h
a, what minimum constant acceleration does the plane require if it is to be airborne after a takeoff run of 240m

b, how long does it take for the plane to become airborne?

thanks so so much :)

This kind of question is dead easy if you just learn three or four simple formulae off by heart that apply to constant acceleration problems.
They are:

s = ut + ft^2/2
s = (u + v)t/2
v^2 = u^2 +2fs

Where
s = distance travelled during constant acceleration (m)
t = time of constant acceleration (seconds)
u = speed at the start of the acceleration (m/s)
v = speed at the end of the acceleration (m/s)
f = acceleration (m/s^2)
All the numbers must be in consistent units of course. I've put examples in brackets.

For the first part you know the distance (s=240 m), the final velocity, v (120 km/h), and the intial velocity u (0 km/h) and you want to find out the acceleration, f. so the equation to use is obviously

v^2 = u^2 +2fs

Rearranging to get f on one side, and putting u=0:

f = v^2/(2s)

Convert the final velocity to m/s:
v = 120 km/h = 120 x 1000 / 3600 m/s = 100/3 = 33.3333 m/s

f = 33.3333^2/(2 x 240) m/s/s
f = 2.3148 m/s/s

b. To find the time required for the plane to become airborne the simplest formula to use is
s = (u + v)t/2

Rearrange to get t on one side of the equation
t=2s/(u+v)
and substitute the known values of u,v and s:

t = 2 x 240 /(0 + 33.33333)
t = 14.4 seconds

Use Vf^2 = Vi^2 + 2ad => a = (Vf^2-Vi^2)/2d = (120^2-0)/(2*0.240km) a= 30,000km/hr^2
30,000km/hr^2*1000m/km*hr^2/3600^2s = 2.315m/s^2 a)
Vf = Vi + a*t => (Vf-Vi)/a = t = (120km/hr-0)/30,000km/hr^2 * 3600s/hr = 14.4s b)