A driver in a moving car applies the brakes. The car slows to a final speed of 2

Question

A driver in a moving car applies the brakes. The car slows to a final speed of 2.20 m/s over a distance of 40.0 m and a time interval of 9.50 s. The acceleration while braking is approximately constant. What is the car's original speed before braking? What is its acceleration during this time? (The car's initial velocity is in the positive direction. Indicate the direction with the sign of your answer.) A cannon fires a shell straight upward; 2.1 s after it is launched, the shell is moving upward with a speed of 16 m/s. Assuming air resistance is negligible, find the speed (magnitude of velocity) of the shell at launch and 4.7 s after the launch. at launch 4.7 s after the launch

Explanation / Answer

intial speed = u
final speed v = 2.20 m/s
distance d = 40 m
time t = 9.50 sec
a)
from the relation
(v+u/2) = d/t
v+u = 2*40/9.50 = 8.42
u = 8.42-2.20= 6.22 m/s
b)
acceleration a = v-u/t = 2.20-6.22/9.50 = -0.42 m/s^2
-------------------------------------
13.
after t = 2.1 s
speed v = 16 m/s
intial speed at lanuch u =?
from
v = u -gt
16 = u -9.8*2.1
u = 36.6 m/s
b)
after 4.7s
v = u -gt = 36.6 - 9.8*4.7 = -9.46 m/s
negative sign indicates moving down towards earth

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