Speed, Time and Distance
- Two ladies simultaneousely leave cities A and B connected by a strainght road and travel towards each other. The first lady travels 2km/h faster than the second lady and reaches B one hour before the second lady reaches A. The two cities A and B are 24 km apart. How many kilometres does each lady travel in one hour ?
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Let the speed of first lady be (v + 2)km/h and speed of second lady will be v km/h.
Total distance = 24 km
For first lady, Speed = Distance/Time
v + 2 = 24/t ...(i)
Let time taken by first lady to cover distance of 24 km be t h.
Then, time taken by second lady to cover same distance will be(t + 1)h.
For second lady, Speed =Distance/time
v = 24/(t + 1) ...(ii)Correct Option: C
Let the speed of first lady be (v + 2)km/h and speed of second lady will be v km/h.
Total distance = 24 km
For first lady, Speed = Distance/Time
v + 2 = 24/t ...(i)
Let time taken by first lady to cover distance of 24 km be t h.
Then, time taken by second lady to cover same distance will be(t + 1)h.
For second lady, Speed =Distance/time
v = 24/(t + 1) ...(ii)
Form Eqs.(i) and (ii), we get
24/t - 2 = 24/(t + 1)
⇒ (24 - 2t)/t = 24/(t + 1)
⇒ (24 - 2t)(t + 1) = 24t
⇒ 24t - 2t2 + 24 - 2t = 24t
⇒ 2t2 + 2t - 24 = 0
⇒ t2 + t - 12 = 0
⇒ t2 + 4t - 3t - 12 = 0
⇒ t(t + 4) -3(t + 4) = 0
⇒ (t - 3)(t + 4) = 0
⇒ t = 3, -4
∴ t = 3 (t ≠- 4)
∴ The distance travelled by the first lady in one hour
= 24/t = 24/3 = 8 km
And distance travelled by the second lady in one hour
= 24/t + 1
= 24/3 + 1 = 6 km
- A thief sees a jeep at a distance of 250 m, coming towards him at 36 km/h. Thief takes 5 seconds to realise that there is nothing but the police is approaching him by the jeep and start running away from police at 54 km/h. But police realise after 10 seconds, when the thief starts running away, that he is actually a thief and gives chase at 72 km/h. how long after thief saw police did police catchup with him and what is the distance police had to travel to do so ?
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Initial speed of police = 10 m/s
Increased speed of police = 20 m/s
Speed of thief = 15 m/s
Initial difference between thief and police = 250 m
After 5 seconds difference between thief and police = 250 - (5 x 10) = 200 m
After 10 seconds more, the difference between thief and police = 200 + (5 x 10) = 250 m.
Now, the time required by police to catch the thief = 250/5 = 50 sec.Correct Option: B
Initial speed of police = 10 m/s
Increased speed of police = 20 m/s
Speed of thief = 15 m/s
Initial difference between thief and police = 250 m
After 5 seconds difference between thief and police = 250 - (5 x 10) = 200 m
After 10 seconds more, the difference between thief and police = 200 + (5 x 10) = 250 m.
Now, the time required by police to catch the thief = 250/5 = 50 s
Distance travelled = 50 x 20 = 1000 m
Total time = 50 + 15 = 65 sec
Total distance = 1000 + (15 x 10) = 1150 m
- Suresh traveled 1200 km by air which formed (2/5) of his trip. One-third of the whole trip he traveled by car And the rest of the journey he performed by train. The distance traveled by train was ?
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Let the total distance be y km.
Then, 2y / 5 = 1200
⇒ y = (1200 x 5) /2 = 3000 km.
Distance traveled by car
= (1/3 X 3000) = 1000 km.Correct Option: B
Let the total distance be y km.
Then, 2y / 5 = 1200
⇒ y = (1200 x 5) /2 = 3000 km.
Distance traveled by car
= (1/3 X 3000) = 1000 km.
Distance traveled by train
= [3000- (1200 + 1000) ] km.
= 800 km.
- Two cyclists A and B start from the same place at the same time. One going toward north at 18 km/hr. and other going toward south at 20 km/hr. What time will they take to be 95 km. apart ?
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Relative velocity = u + v = 18 + 20 = 38 km
They are 38 km. apart in 1 hr.Correct Option: D
Relative velocity = u + v = 18 + 20 = 38 km
They are 38 km. apart in 1 hr.
∴ They will be 95 km. apart in ( 95 / 38) hrs.
= 2 hrs . 30 min
- A bullock cart has to cover a distance of 80 km. in 10 hours. If it cover half of journey in 3/5th time, what should be its speed to cover the remaining distance in time left ?
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Distance left = (1/2 x 80 ) km. = 40km.
Time left - [(1-3/5) x 10 ] hrs.
= 4 hoursCorrect Option: D
Distance left = (1/2 x 80 ) km. = 40km.
Time left - [(1-3/5) x 10 ] hrs.
= 4 hours
Required speed = (40 / 4 ) km/hr
= 10 km/hr.