## Thursday, 17 March 2011

### Speed, Time and Distance

Speed, Time and Distance
• Speed is the distance covered by an object in unit time.
• Speed = distance / time
• Distance = speed × time
• If distance is fixed, then speed and time are inversely related.
More the speed, less is the time taken and vice versa.
• To convert m/sec into km/hour, multiply by 18/5; to convert km/hour into m/sec, multiply by 5/18
• Average speed is found by dividing total distance covered by total time taken.
Exercise
1. A car is travelling at an average speed of 36 km/hour. How much distance will it travel in 45 minutes?
2. A bullock cart is moving at an average speed of 6 km/hour. How much time will it take to cover distance of 20 kilometers?
3. A cat runs at a speed of 100 meters in a minute. Find its speed in km/hour.
4. Convert the following speeds into m/sec
(a) 72 km/hour
(b) 1.2 km per minute
(c) 600 meters per hour.
5. Convert the following speeds into kms/hour
(a) 15 m/sec
(b) 1.5 m/sec
(c) 500 meters per minute.
6. An airplane is flying at a speed of 720 km/hour.
(a) If the aerial distance between two cities is 1800 kms, how much time will the airplane take?
(b) How much distance does the airplane cover in 40 minutes?
(c) How far will it fly in 15 seconds?
7. Liza and Tanya leave the same camp and run in opposite directions. Liza runs at 2 m/s and Tanya at 3 m/s. How far apart are they after 1 hour?
8. Two cars are 635 kilometers apart. They start at the same time and drive toward each other. One travels at 70 km/hr and the other travels at 57 km/hr. In how many hours do they meet?
9. A man can swim at 6 km/hour. The speed of a stream is 2 km/hour. How much time will the man take to swim 400m if
(a) he is swimming with the stream?
(b) he is swimming against the stream?
10. A tram travels at 10 km/hour for 2 hours and then at 13 km/hour for 1 hour. Find its average speed.
11. A cyclist travels at 8 km/hour for 15 minutes and then at 6 km/hour for 25 minutes. Find his average speed.
12. At a movie set, a horse gallops away with heroine at a speed of 60 km/hour for some time before the hero jumps on its back from a tree and brings the horse to a comfortable trot of 12 km/hour. If in total 26 minutes, the horse covered a distance of 10 kms, calculate for how much distance and time the horse galloped and trotted?
13. A monkey and an ass went for a race. The monkey ran at a speed of 6 km/hour but the ass started running backwards at a speed of 1m/sec. Determine the distance between them after 5 minutes.
14. A train covered first 150 kms at a speed of 50 kms an hour and then covered the remaining 150 kms in 2 hours. Find its average speed.
1. 27 kms                        2. 3 hours 20 minutes
3. 6 km/hour
4. (a) 20 m/sec                (b) 20 m/sec             (c) 1/6 m/sec
5. (a) 54 km/hour            (b) 5.4 km/hour        (c) 30 km/hour
6. (a) 2½ hours               (b) 480 km               (c) 3 km
7. 18 kilometers             8. 5 hours
9. (a) 3 minutes             (b) 6 minutes
10. 11 km/hour              11. 6.75 km/hour
12. The horse galloped 6 kms in 6 minutes and then trotted 4 kms in 20 minutes.
13. 800 meters               14. 60 km/hour