L11 : Questions 2 - Motion and Time, Science, Class 7 Video Lecture

hello friends this video on motion and
time part 11 is brought to you by Sam
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question number 6 Salma takes 15 minutes
from a house to reach her school on a
bycicle
if the bicycle has a speed of 2 meter
per second calculate the distance
between her house and the school so
let's say this is her house and this is
her school so we have to find out the
distance between the two so the time
taken by her to reach her school is 15
minutes and the speed of her bicycle is
2 meters per second so the speed is
given as 2 meter per second and time
taken is even as 15 minutes so one
minute is equal to 60 seconds so 15 into
60 seconds you can convert it from
minutes to seconds so this is going to
be 900 seconds so now we know that speed
is equal to distance by time so
therefore we can say this tense is equal
to speed into time so that is equal to 2
into 900 which is equal to 1800 meters
or we can write it as 1 point 8
kilometres so this is the distance
between her house and TSP question
number 7 show the shape of the distance
time graph for the motion in the
following cases a car moving with a
constant speed so the speed of the car
is constant the car is moving and the
speed is also constant so in distance
time graph this is the distance and this
is the time so any car moving with a
constant speed is nothing but uniform
motion and how the graph looks like in
uniform motion so this is how the graph
would be would be a straight line so
that it covers equal distances in equal
intervals of time a car part of the side
of the road parked on the
means no motion the particles not moving
at all the time is not moving at all it
is at rest so in the second case if this
is distance and this is time so this is
how the plot would be because the
distance value of distance would not
change with increase in time question
number eight which of the following
relations is correct speed is equal to
distance into time speed is equal to
distance by time speed is equal to time
by distance and speed is equal to 1 by
distance into time so speed is always
distance per unit time so second one is
the right option question of my name the
basic unit of speed is kilometer per
minute minute meter per minute kilometer
per hour meter per second so the basic
unit would be meter per second that's
because as I have mentioned before that
speed is distance per unit time and SI
unit for distances meter then SI unit
for time is seconds so therefore the
basic unit for speed would be meter per
second question number 10 a car moves
with a speed of 40 kilometers per hour
for 15 minutes and then with a speed of
60 kilometers per hour for the next 50
minutes so the total distance covered by
the car is so here as for this question
it says that for the first 15 minutes so
the first 15 minutes the car moves with
a speed of 40 kilometers per hour the
next 15 minutes it moves with a speed of
60 kilometers per hour so we have to
find out the total distance so let's say
that for the first 50 minutes
the distance travelled is d1 for the
next 15 minutes the distance traveled is
deep so we have to find out d1 and d2
and then
and add them together to find out the
total distance so what would be demon so
distance will be equal to speed into
time so what is the speed speed is 40
kilometer per hour and time is 15
minutes so we will convert this also
into hour so 15 by 60 so this would be 4
so this is equal to 10 kilometers
similarly let's find out d2 which will
be equal to speed into time speed is 60
kilometer per hour and time is again 15
minutes which is 15 by 60 so this would
be 4 so this will be again 15 kilometers
so d1 and d2 are 10 and 15 kilometers
therefore the total distance would be
equal to d1 plus d2 which is equal to 10
plus 15 that is 25 kilometers so 25
kilometers would be the right answer
question number 11 the figure shows the
distance time graph for the motion of
two vehicles a and B which one of them
is moving faster now how do we get to
know the speed of a vehicle from the
distance time graph the slope tells us
the speed slope steeper the slope
greater the speed so if you compare the
slope of a and B the slope of a is more
than the slope of B so you just consider
any point so let's say you just consider
this point you draw a straight line on
the x-axis so this line crosses through
this point on a and this point on B so
for this point what would be the speed
at this point let's say this is p1 and
this is p2 so for t1 what would be the
speed at p1 so speed at p1 let's
calculate speed at Point P 1 so speed at
Point P 1 would be equal to distance
traveled by time taken so let's say this
is T and let's say this is D let's say
this is t1 and this is d1 so this would
be equal to distance traveled that is d
1 by t1 now similarly let us try to
calculate speed
we do that is this point so this would
be equal to this much distance so this
distance is let's say D 2 so this will
be equal to D 2 by T 1 because time
remains the same now if you compare D 1
and D 2 looking at this picture
you can see that D 1 is greater than D 2
correct
therefore speed at P 1 is greater than
speed at people so that means if you
compare any two corresponding points on
a and B the speed for the point which is
lying on a will always be more that
means the vehicle a is moving faster so
a is faster than B so with this we have
reached towards the end of this lesson
on motion and I hope that this lesson
would have helped you so see you all in
the next lesson thank you please visit
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