Question

please help me in solving this question
request to all seniors

Answer 1

it is mentioned that the object was at rest from 9 a.m. and came to motion at 9:30 a.m.
so,
there was not at all any movement of the object from 9 a.m. to 9:30 a.m.

And the object came to motion at 9:30 a.m. and travelled at a constant velocity of 10 km per hour till 10 a.m. That is equal to half hour and further that is 30 minutes.

now there are two parts of the questions the first part wants to know the average speed of the object between 9 a.m. to 10 a.m.
and the second part wants to know the average speed of the object from 9:15 a.m. to 10 a.m.

now let's start with the first part

now from 9 a.m. to 9:30 a.m. there is no motion in the object.
hence the distance covered will be equal to zero and the time taken is equal to half hour

in the next half hour that is from 9:30 a.m. to 10 a.m. object travels with a velocity of 10 km per hour.
So now,
finding the distance which object travelled in this particular time.

Distance = speed * time
So,
D = 10 km/hr * 1/2 hr = 5km

hence the total distance travelled from 9 a.m. to 10 a.m. equal to 0 + 5 is equal to 5 km

the time taken is equal to half hour + half hour is equal to 1 hour

Hence,
to find average speed, the thing which we found are as follows :-

Total distance = 5 km
Time taken = 1 hour

so we know that average speed is equal to :-

$\frac{total \: distance}{time} \\ \\ = \frac{5}{1} = 5$
since the average speed of the object from 9 a.m. to 10 a.m. equal to 5 km per hour.

now let's move to the second part where we have to find the average speed of the object from 9:15 a.m. to 10 a.m.

change the object pass address from 9 a.m. to 10 a.m. the distance covered from 9:15 a.m. to 9:30 a.m. will be equal to 0 km and the time taken for this is equal to 15 minutes which is equal to 1 / 4 hours.


now,
in the second part everything remains constant as the object was in motion with average speed of 10 km per hour for 30 minutes.
hence, in the above we found the distance travelled in this half an hour is equal to 5 km

now the total distance travelled is equal to 5 km and the total time taken is equal to 1/4 + 1/2 = 3/4 hours

we have got all the basic requirements which we need to find the average speed of an object
so,
finding the average speed of the object

$\frac{5}{ \frac{3}{4} } \\ \\ = \frac{5 \times 4}{3} = \frac{20}{3} \\ \\ = 6. 66666666 ... \\ \\ = 6.67(approx)$

Hence,
average speed of the objects in this particular time is equal to 6.67 km per hour.