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Q.1. A car travels first half distance between two
places with a speed of 40 km/h and the rest
half distance with a speed of 60 km/h. The
average speed of the car will be -
[a] 100 km/hr [b]50km/hr
C]48km/hr
[d]200km/hr
plz help me....
Answers
Let the total distance travelled by the car be d.
According to the question,
The car travelled half of the distance with speed 40 km/h and the other half with speed 60 km/h.
Case 1
Distance travelled = d/2
⇒ Distance = Speed × Time
⇒ d / 2 = 40 × t₁
⇒ t₁ = d/80 ...(1)
Case 2
Distance travelled = d/2
⇒ Distance = Speed × Time
⇒ d / 2 = 60 × t₂
⇒ t₂ = d / 120 ...(2)
Now, We have to find the average speed of the car:
⇒ Avg. Speed = Total Distance travelled / Total Time taken
⇒ Avg. Speed = d / (t₁ + t₂)
⇒ Avg. Speed = d / (d/80 + d/120) [ from (1) & (2) ]
⇒ Avg. Speed = d / (3d + 2d)/240
⇒ Avg. Speed = 240d / 5d
⇒ Avg. Speed = 240 / 5
⇒ Avg. Speed = 48 km/h
So, The average speed of the car is 48 km/h
∴ Option C is correct.
Some Information :-
☛ Speed is the rate of change in distance per unit time, It is a scalar quantity. which means It doesn't have any direction.
☛ Average Speed is the ratio of total distance travelled to total time taken.
Answer:
[b] 50 km/hr
Explanation:
1) AS THE DIST. IS SAME BETWEEN BOTH THE SPEEDS , WE WILL NOT CONSIDER THE DISTANCE
2) THEREFORE , BY TAKING THE MEAN OF THE SPEEDS WE GET THAT:
MEAN= SUM OF QUANTITIES
__________________
NO. OF QUANTITIES
= 40+60
______
2
=50 km/hr
HOPE IT HELPS
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