Athletic competition

In a 400 meter athletic competition, a participant covers the distance as given below.
find the average speed?

first 80 meters 10 m/s
next 240 meters 7.5 m/s
last 80 meters 10 m/s

Correct result:

v =  8.3333 m/s

Solution:

$$\begin{gathered} s=vt \\ {s}_1=80\text{ m } \\ {s}_2=240\text{ m } \\ {s}_3=80\text{ m } \\ {v}_1=10\text{ m/s } \\ {v}_2=7.5\text{ m/s } \\ {v}_3=10\text{ m/s } \\ {t}_1=s_1\mathrm{/}{v}_1=80\mathrm{/}10=8\text{ s } \\ {t}_2=s_2\mathrm{/}{v}_2=240\mathrm{/}7.5=32\text{ s } \\ {t}_3=s_3\mathrm{/}{v}_3=80\mathrm{/}10=8\text{ s } \\ v={\displaystyle \frac{s_1+s_2+s_3}{t_1+t_2+t_3}}={\displaystyle \frac{80+240+80}{8+32+8}}={\displaystyle \frac{25}{3}}=8.3333\text{ m/s} \end{gathered}$$

Try another example

Showing 0 comments:

Next similar math problems:

• Fog
  The car started in fog at speed 30 km/h. After a 12-minute drive, the fog dissipated and the driver drove next 12 minutes distance 17 km. On the last 17 km long again the driving conditions deteriorated and the driver drove the speed of 51 km/h. a) Calcul
• Two cities
  The car goes from city A to city B at an average speed of 70 km/h, back at an average speed of 50 km/h. If it goes to B and back at an average speed of 60 km/h, the whole ride would take 8 minutes less. What is the distance between cities A and B?
• Express train
  International express train drove from Kosice to Teplice. In the first 279 km, the track was repaired, and therefore it was moving at a speed of 10km/h less than it was scheduled to drive. The rest of the 465 km trip has increased the speed by 8 km/h than
• Speed of Slovakian trains
  Rudolf decided to take the train from the station 'Ostratice' to 'Horné Ozorovce'. In the train timetables found train Os 5409 : km 0 Chynorany 15:17 5 Ostratice 15:23 15:23 8 Rybany 15:27 15:27 10 Dolné Naštice 15:31 15:31 14 Bánovce nad Bebravou 15:35 1
• Average
  What is the average speed of the car, where half of the distance covered passed at speed 66 km/h and the other half at 86 km/h.
• Motorcyclist
  From Trutnov, the motorcyclist started at an average speed of 60km/hour. At 12.30hrs the passenger car was started at a speed of 80km/hour. How many hours and at what distance from Trutnov will car catch a motorcycle?
• Overtaking
  On the direct road, the passenger car overtakes the slower bus by starting to overtake 20 meters from the bus and after passing it ahead of it again 20 meters away. The car overtakes at a steady speed of 72 km/h, the bus goes at a steady speed of 54 km/h.
• Constant motion
  The car has undergone constant motion 120 km in 1 hour 30 minutes. Determine its average speed. Determine how long car drove in the first 20 minutes and 50 minutes from the start of the move.
• Between two bus stops
  Wanda lives between two bus stops at three-eighths of their distance. He started the house today and found that whether he was running to one or the other stop, he would have arrived at the bus stop. The average bus speed is 60 km/h. What is the average s
• Car
  Car goes from point A to point B at speed 86 km/h and back 53 km/h. If they goes there and back at speed 67 km/h trip would take 10 minutes shorter. What is distance between points A and B?
• Collision
  The two bodies, whose initial distance is 240 m, move evenly against each other consistently. The first body has an initial velocity of 4 m/s and an acceleration of 3 m/s², the second body has an initial speed of 6 m/s and an acceleration of 2 m/s². Fin
• Two cyclists 2
  At the same time, two cyclists left the towns A and B at constant speeds. The first one going from town A to town B, and the second one from town B to town A. At one point of the trip they met. After they met, the first cyclist arrived at town B in 36min,
• Car - road
  Car started at 11:40 at speed 54 km/h from A and to B arrived at 12:20. Determine the distance A and B.
• Car overtaking
  A passenger car travels at a speed of 30 m/s, and before it travels freight truck that drives at a constant speed of 10 m/s. Within 30 meters of the truck, the driver of the car finds out that the truck can not overtake. That's why it starts braking with
• Motion
  The two bodies move in the same direction evenly in a straight line, at speeds of 5 cm/s and 10 cm/s. The movement of the first body started 2 seconds earlier than the movement of the second body, from a point located at a distance of 20 cm from the start
• Znojmo
  From Znojmo to Brno started truck with a trailer at an average speed 53 km per hour. Against him 14 minutes later from Brno started car with an average speed of 1.2-times greater than the truck. How long and how far from Znojmo, they meet if the distance
• Two trains
  Two trains go at each other. First at speed 40 km/h and the second at speed 60 km/h. At what distance will be 30 minutes before they will meet?