Uniformly accelerated linear motion downwards

  • Thread starter Andrei0408
  • Start date
  • #1
50
8
Homework Statement:
A small body is freely released from a platform located 605 meters above the ground. If g=10m/s2
and
we ignore air resistance find:
a) the time required to reach the ground;
b) the velocity at the ground;
c) the
velocity at 425 m from the ground;
d) the distance traveled in the first 4 seconds of flight;
e) the distance
traveled in the last 4 seconds of flight;
f) the distance traveled in the third second of flight and in the
seventh.
Relevant Equations:
motion law, velocity law
Could you check if what I did is right and help me at e) and f)? Thank you!
 

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Answers and Replies

  • #2
50
8
Homework Statement:: A small body is freely released from a platform located 605 meters above the ground. If g=10m/s2
and
we ignore air resistance find:
a) the time required to reach the ground;
b) the velocity at the ground;
c) the
velocity at 425 m from the ground;
d) the distance traveled in the first 4 seconds of flight;
e) the distance
traveled in the last 4 seconds of flight;
f) the distance traveled in the third second of flight and in the
seventh.
Relevant Equations:: motion law, velocity law

Could you check if what I did is right and help me at e) and f)? Thank you!
EDIT: I tried e) again and got this:
tAD = tAO - 4
tAD = 7s
yDO = yA - 1/2 * g * (tAD)^2
yDO = 605 -245
yDO = 360m
is this right?
 
  • #3
337
142
•It seems to me that d. part is not correct.

•distance travelled in nth second means distance travelled between time interval of ##n-1## to ##n## seconds.

•e part—>
If total time interval is t seconds and you want to find the distance traveled in last n seconds you can calculate the the distance traveled in time interval of ##t-n## seconds and then subtract it from distance traveled in total time interval.
 
  • #4
50
8
•It seems to me that d. part is not correct.

•distance travelled in nth second means distance travelled between time interval of ##n-1## to ##n## seconds.

•e part—>
If total time interval is t seconds and you want to find the distance traveled in last n seconds you can calculate the the distance traveled in time interval of ##t-n## seconds and then subtract it from distance traveled in total time interval.
Thank you!
 
  • #5
Lnewqban
Gold Member
1,254
708
EDIT: I tried e) again and got this:
tAD = tAO - 4
tAD = 7s
yDO = yA - 1/2 * g * (tAD)^2
yDO = 605 -245
yDO = 360m
is this right?
That result seems to be correct.

After following your work for a), b), c) and d), I believe that you take many steps that are not necessary and could introduce errors.

For resolving f), you could calculate the velocities at times 2 seconds and 7 seconds first.
Then, include each of those values into the equation to calculate the distance traveled during the following second.
 
  • #6
50
8
That result seems to be correct.

After following your work for a), b), c) and d), I believe that you take many steps that are not necessary and could introduce errors.

For resolving f), you could calculate the velocities at times 2 seconds and 7 seconds first.
Then, include each of those values into the equation to calculate the distance traveled during the following second.
Thank you, I'll try to be more careful
 

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