As a runner crosses the finish line of a race, she starts decelerating from a velocity of 9 m/s at a rate of 2 m/s^2. take the runner's velocity as she crosses the finish line to be in the positive direction. what is the runner’s displacement, in meters, during the first 5 seconds after crossing the finish line?
what is her velocity, in meters per second, 5 seconds after crossing the finish line?
- 1 m/s, 20 m
u = 9 m/s, a = - 2 m/s^2, t = 5 sec
Let s be the displacement and v be the velocity after 5 seconds
Use first equation of motion.
v = u + a t
v = 9 - 2 x 5 = 9 - 10 = - 1 m/s
Use second equation of motion
s = u t + 1/2 a t^2
s = 9 x 5 - 1/2 x 2 x 5 x 5
s = 45 - 25 = 20 m
a longitudinal wave moves energy that is to the direction of the wave’s movement. - true