average velocity and finding displacement

[jaker904]

hello folks got a problem here. speed of an object increases uniformly from 36 km/h to 108km/h in 20 seconds

now the problem im having is figuring the displacement. do i simply subract 36 from 108? giving me 72. divide that by 20s =average velocity?

 

[DrPhil]

hello folks got a problem here. speed of an object increases uniformly from 36 km/h to 108km/h in 20 seconds

now the problem im having is figuring the displacement. do i simply subract 36 from 108? giving me 72. divide that by 20s =average velocity?

Since the increase of speed (i.e., acceleration) was uniform, the average velocity is simply the average of the initial and final velocities:
\(\displaystyle v_{avg} = (v_i + v_f)/2\)

Use that average velocity to find displacement. Take care with the units.

 

[Deleted member 4993]

hello folks got a problem here. speed of an object increases uniformly from 36 km/h to 108km/h in 20 seconds

now the problem im having is figuring the displacement. do i simply subract 36 from 108? giving me 72. divide that by 20s =average velocity?

Use Galileo's first equation:

v = u + a * t

Use Galileo's third equation:

v² = u² + 2 * a * s

where:

s = displacement

u = initial velocity

v = final velocity

a = acceleration

t = time elapsed

 

[Bob Brown MSEE]

What to do?

hello folks got a problem here. speed of an object increases uniformly from 36 km/h to 108km/h in 20 seconds

now the problem im having is figuring the displacement. do i simply subract 36 from 108? giving me 72. divide that by 20s =average velocity?

When working problems that involve distance, velocity and acceleration -- DRAW A VELOCITY DIAGRAM.
Don't memorize formulas -- just remember.
time = x axis
velocity = y axis
acceleration = slope
distance = area


"speed of an object increases uniformly" means a straight line. (uniform acceleration is constant slope)
Distance between time=0 and time=20sec is the area under the curve.
The area of this trapezoid is (v1+v2)/2*t.

WATCH OUT: units are inconsistent See why? Know what to do about it?