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NCERT Solutions Class 7 Science Solutions for Exercise in Chapter 13 - Motion and Time
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A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is:
(i) 100 km (ii) 25 km (iii) 15 km (iv) 10 km
Answer:
The answer is (ii) 25 km
Calculation:
When the speed of the car is 40 km/h
Time taken = 15 min = 15/60 = 0.25 h
Distance covered d1 = speed x time taken
= 40 x 0.25 = 10 kms
When the speed of the Car is 60 km/ h
Distance covered d2 = speed x time taken
= 60 x 0.25= 15 kms
Total distance covered by the car = d1 + d2
= 10 + 15
= 25 kms
Video transcript
"hello everyone i am sumanjali science
tutor from lido learning
welcome to the question and answer
session in our today's question there is
a problem given
a car moves with a speed of 40 kilometer
per hour for 15 minutes
and then with a speed of 60 kilometer
per hour for the next
15 minutes the total distance covered by
the car
is dash we need to find out the distance
so before going to the answer let us
have an idea about
what is a speed so speed is nothing but
so speed is nothing but it was the
distance covered by
distance covered
in time we can calculate
speed by using formulae speed is equals
to
distance divided by time
and the unit of speed is kilometer
per hour or meter per second also we can
calculate in meter per second also but
in the given question the speed was
given in
40 kilometer per hour and 60 kilometer
per hour
so we are taking speed uh speed units in
kilometer per hour in this
the distance units are in kilometer and
the time units
are in hour let us move to the question
a car moves with a speed of 40 kilometer
per hour
so let us consider a car starting point
here as a okay so car is moving
moving with a speed of 40 kilometer per
hour
up to point b so here speed
is given speed is equals to 40 kilometer
per hour
for for 15 minutes so
time is equals to 15 minutes
and this is point b from point b uh
car is again started and it reaches to
point
c and it reaches to point c
with a speed of with a speed of
60 kilometer per hour
for time is equals to 15 minutes in both
the cases we need to calculate a
distance
so we can take distance 1
as d1 and distance 2 as
d2 okay so from the formulae from the
formula the
distance is in kilometer and the time
is in hour so but here the time given uh
in 15 minutes so we need to convert this
time
into our okay so time is equal to 15
minute and we need to if we want to
convert
this into our so we need to divide it
with
60 because 1 hour is equals to because
1 hour is equals to 60 minute
so 1 minute is equal to 1 minute is
equal to 1
divided by 60 so that 15 minute
is equals to 15 divided by
60 so 15 divided by 60 15
ones are 15 fours are 15
so 1 divided by 4 it is equals to
0.2525 hour
and in the second case and in the second
case
time is equals to this is in the first
case
this is in the second case time is
equals to here also it is 15 minutes
15 divided by 60 same 0.25
hour okay now let us calculate
distance one okay so distance one
distance is equals to distance
is equals to speed multiplied by
time speed multiplied by time
for first case for first case d1 is
equals to
its speed value 40 multiplied by
time value 0.25
so if you multiply this we will be
getting we will be getting
10 kilometer and
in the second case d2 is equals to
60 multiplied by
0.25 that is
60 multiplied by 1 by 4
1 by 4 so four ones are four
fifteen zero four ones are four four
fifteen zero
sixty so it is fifteen kilometer
so now the total distance total distance
is equals to
ten plus fifteen kilometer is equals to
25 kilometer is the answer
so given total distance
covered by car is 25 kilometer
is answer
if you have further queries reach us at
the comment section
and please subscribe to our channel
leader learning question and answer
for further queries thank you"
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