Studying for exams need help very soon

  • Thread starter thschica
  • Start date
  • #1
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Studying for exams need help very soon!!!!

On both of these I got the right answer but it was so long ago I have no idea how to do them.
(Which equation am I to use?)(v=Vo+at? if so how?)
1.Determine the stopping distances for an automobile with an initial speed of 91 km/h and human reaction time of 3.0 s for the following accelerations.
(a) a = -4.0 m/s2
? m
(b) a = -8.0 m/s2
? m
(This one is beyond me I keep attempting to use equations but none of them are working)
2.5. A football is kicked at ground level with a speed of 20.0 m/s at an angle of 38.0° to the horizontal. How much later does it hit the ground?
? seconds
 

Answers and Replies

  • #2
kp
53
0
a) use a kinematic equation to solve for "d"
, then use a kinematic equation to solve for "time"
then add reaction time.

b) resolve the components (sin & cos)
the y component give you time
 
  • #3
Astronuc
Staff Emeritus
Science Advisor
18,824
2,052
The stopping distance consists of two parts, the distance traveled before the deceleration is applied, which is given by x1 = v tr, where r would be the response time, and then the distance traveled during the period of deceleration, which is governed by a different equation.

see - http://hyperphysics.phy-astr.gsu.edu/hbase/mot.html#mot1
for linear motion in one dimension.
 

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