# Critical Sum of Speed Time and Distance Class 7

Solution 1.

Case 1:

Data given:

Distance between station A and B = 120 km

Time taken by the train = 2 h 30 minutes

=(2+30/60) h

=5/2 h

Speed S1 of the train in km/h = D/S

=120/(5/2)

=48 km/h

Case 2:

Distance between station A and B = 120 km

Time taken by the train = 2 h

Speed S2 of the train = 120/2

=60 km/h Increased speed (S2-S1) = (60-48) km/h

=12 km/h Ans.

Question 2. Two trains start from the same staion in the smae direction. The speed of the first train is 70 km/h and that of the second train is 20 m/s. 1) Which train is moving faster ?

2) What is the distance between the trains after 1 hour and 15 minutes ?

Answer 2. Speed of the first train = 70 km/h

Speed of the second train = 20 m/s

i)Speed of the second train in km/h= 20x(18/5)

= 72 km/h

Therefore the second train is moving faster.

ii) Time = 1 h 15 m

=(1+15/60)h

=1+1/4 h

5/4 h

Distance covered by the first train= DXS

=70 X 5/4

87.5 km

Distance covered by the second train in the same time = D X S

= 72 X 5/4 km

90 km

Therefore the distance between two train after 1 h 15 minutes will be (90-87.5 ) km

=2.5 km Ans.

Question 3. Mohan could run a 100-m race in 20 seconds. After training , he can finish the race in 15 seconds. By how much has he improved his speed? ?

Answer 3. Speed of Mohan = D/ S

=100/20

5 m/s

Time taken to complete the race after training = 15 s

Speed of Mohan after training = 100/15 m/s

20/3 m/s

Improvement = (20/3 -5 )

=5/3 m/s

1 2/3 m/s or 1.67 m/s Ans.