Advertisements
Advertisements
प्रश्न
The speed of a boat in still water is 15 km/h and speed of stream is 5 km/h. The boat goes x km downstream and then returns back to the point of start is ______.
विकल्प
`(x/20 - x/5)` hrs
`(x/10 - x/20)` hrs
`(x/20 + x/10)` hrs
`(x/20 - x/10)` hrs
उत्तर
The speed of a boat in still water is 15 km/h and speed of stream is 5 km/h. The boat goes x km downstream and then returns back to the point of start is `underlinebb((x/20 + x/10) hrs)`.
Explanation:
Given the speed of boat in still water = 15 km/h
Speed of stream = 5 km/h
∴ Speed of boat upstream
= 15 – 5
= 10 km/h
And the speed of boat downstream
= 15 + 5
= 20 km/h
∴ Time is taken by boat x km downstream
@ 20 km/h = `"Distance"/"Speed"` = `x/20` hrs
Time is taken by boat x km upstream
@ 10 km/h = `x/10` hrs
Thus, the total time taken by boat goes x km downstream and then return to the point of start = `(x/20 + x/10)` hrs.
संबंधित प्रश्न
A car covers a distance of 400 km at a certain speed. Had the speed been 12 km/h more, the time taken for the journey would have been 1 hour 40 minutes less. Find the original speed of the car.
If the speed of an aeroplane is reduced by 40 km/hr, it takes 20 minutes more to cover 1200 km. Find the speed of the aeroplane.
A goods train leaves a station at 6 p.m., followed by an express train which leaved at 8 p.m. and travels 20 km/hour faster than the goods train. The express train arrives at a station, 1040 km away, 36 minutes before the goods train. Assuming that the speeds of both the train remain constant between the two stations; calculate their speeds.
The distance by road between two towns A and B is 216 km and by rail it is 208 km. A car travels at a speed of x km/hr and the train travels at a speed which is 16 km/hr faster than the car. Calculate:
- the time taken by the car to reach town B from A, in terms of x;
- the time taken by the train to reach town B from A, in terms of x.
- If the train takes 2 hours less than the car, to reach town B, obtain an equation in x and solve it.
- Hence, find the speed of the train.
Two trains leave a railway station at the same time. The first train travels due west and the second train due north. The first train travels 5 km/hr faster than the second train. If after 2 hours, they are 50 km apart, find the speed of each train.
An aeroplane travelled a distance of 400 km at an average speed of x km/hr. On the return journey, the speed was increased by 40 km/hr. Write down an expression for the time taken for:
- the onward journey;
- the return journey.
If the return journey took 30 minutes less than the onward journey, write down an equation in x and find its value.
A car travels a distance of 72 km at a certain average speed of x km per hour and then travels a distance of 81 km at an average speed of 6 km per hour more than its original average speed. If it takes 3 hours to complete the total journey then form a quadratic equation and solve it to find its original average speed.
The speed of a boat is 32 km/h. If the speed of stream is 8 km/h, the speed of boat upstream is ______.
The speed of train A is x km/h and speed of train B is (x – 5) km/h. How much time will each train take to cover 400 km?
A car is moving with a speed of 100 km/h. If the speed of car first increases by x% and then decreases by x%, the final speed of the car is 96 km/h. The value of x is ______.
