maybe u should use this formula
s=1/2(v+u)t
s is displacement
v is initial velocity
u is final velocity
t is time
s=1/2(90+70)2
Hi all
who I can find the displacement in this Q ?
A jetliner lands with a speed of 90 m/s on runway . It runs with constant speed for 2 s , before the brakes are applied . The brakes produce a deceleration of 20 m/s2 . What is its displacement on the runway .
I try to solve
V0 = 90 m/s
t1 = 2s
x = V0 X t1 = 180 m
a = -20 m/s2
then I don't know who I complte it ?
Hi,
You could try drawing a rough graph, then calculate the area under the graph for the total distance
It starts at 90m/s, so in a speed time graph there is a horizontal line at 90 for 2 sec. Then the line slopes downwards, losing 20m's every second, so in 4.5 seconds it has a speed of 0.
When you calculate the area under the graph:
2x90 + (6.5-2)x90x0.5 = 382.5m
There is a general rule that the area under a speed time graph is the distance traveled. So off course you can just calculate the area under it just like calculating the area of a square and triangle.
Because the deceleration is 20 meters per second per second, this means that a speed of 20meters per second is lost every second. So it takes 4.5 seconds for a speed of 90m/s to reach 0m/s (90/20 = 4.5)