Speed, Time and Distance
- Two rifles are fired from the same place at a difference of 11 min. 45 seconds. But a man who is coming towards the same place in a train hears the second sound after 11 minutes. Find the speed of the train (Assuming speed of sound = 330 m/s).
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Difference of time = 11 minutes 45 seconds – 11 minutes = 45 seconds
Distance covered by sound in 45 seconds = Distance covered by train in 11 minutes
⇒ 330 × 45 = 11 × 60 × Speed of train⇒ Speed of train = 
330 × 45 
m/sec. 11 × 60 = 45 × 18 kmph. 2 5
= 81 kmph.Correct Option: C
Difference of time = 11 minutes 45 seconds – 11 minutes = 45 seconds
Distance covered by sound in 45 seconds = Distance covered by train in 11 minutes
⇒ 330 × 45 = 11 × 60 × Speed of train⇒ Speed of train = 330 × 45 m/sec. 11 × 60 = 45 × 18 kmph. 2 5
= 81 kmph.
- A man can cover a certain distance in 3 hours 36 minutes if he walks at the rate of 5 km/hr. If he covers the same distance on cycle at the rate of 24 km/hr, then the time taken by him in minutes is
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Distance covered in 3 hours 36 minutes
i.e. 3 36 hours 60 i.e. 3 3 hours 5 = 5 × 18 = 18 km. 5
∴ Time taken at 24 kmph.= 18 hour 24 = 18 × 60 minutes 24
= 45 minutesCorrect Option: B
Distance covered in 3 hours 36 minutes
i.e. 3 36 hours 60 i.e. 3 3 hours 5 = 5 × 18 = 18 km. 5
∴ Time taken at 24 kmph.= 18 hour 24 = 18 × 60 minutes 24
= 45 minutes
- Due to inclement weather, an air plane reduced its speed by 300 km/hr, and reached the destination of 1200 km late by 2hrs. Then the schedule duration of the flight was
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Let the original speed of aeroplane be x kmph.
According to the question,1200 − 1200 = 2 x − 300 x ⇒ 1200 x − x + 300 = 2 x(x − 300) ⇒ x (x – 300) = 1200 × 300 2
⇒ x (x – 300) = 600 × 300
⇒ x (x – 300) = 600 (600 – 300)
⇒ x = 600 kmph.∴ Scheduled duration of flight = 1200 = 2 hours 600 Correct Option: C
Let the original speed of aeroplane be x kmph.
According to the question,1200 − 1200 = 2 x − 300 x ⇒ 1200 x − x + 300 = 2 x(x − 300) ⇒ x (x – 300) = 1200 × 300 2
⇒ x (x – 300) = 600 × 300
⇒ x (x – 300) = 600 (600 – 300)
⇒ x = 600 kmph.∴ Scheduled duration of flight = 1200 = 2 hours 600
- A motor cycle gives an average of 45 km per litre. If the cost of petrol is Rs. 20 per litre, the amount required to complete a journey of 540 km is, (in Rupees)
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Consumption of petrol in covering 540 km
= 540 = 12 litres 45
∴ Required expenses
= Rs. (12 × 20)
= Rs. 240Correct Option: D
Consumption of petrol in covering 540 km
= 540 = 12 litres 45
∴ Required expenses
= Rs. (12 × 20)
= Rs. 240
- Two guns are fired from the same place at an interval of 6 minutes. A person approaching the place observes that 5 minutes 52 seconds have elapsed between the hearing of the sound of the two guns. If the velocity of the sound is 330 m/sec, the man was approaching that place at what speed (in km/hr) ?
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Difference of time
= 6 min. – 5 min. 52 sec.
= 8 seconds
Distance covered by man in 5 min.52 seconds
= Distance covered by sound in 8 seconds
= 330 × 8 = 2640 m.∴ Speed of man = 2640 m 5 min. 52 sec. = 2640 m/sec 352 = 2640 × 18 kmph 352 5
= 27 kmphCorrect Option: B
Difference of time
= 6 min. – 5 min. 52 sec.
= 8 seconds
Distance covered by man in 5 min.52 seconds
= Distance covered by sound in 8 seconds
= 330 × 8 = 2640 m.∴ Speed of man = 2640 m 5 min. 52 sec. = 2640 m/sec 352 = 2640 × 18 kmph 352 5
= 27 kmph
