Question

Ракета за 4 секунды пролетела 28 км.Затем её скорость увеличилась на 3 км/сек.Найдите скорость ракеты в в конце пятой секунды.

Answer 1

1)28*4=112(км) 2)28+3=31(км) 3)112+31=143(км) Ответ:143 км/с

Answer 2

Problem Analysis

We are given that a rocket traveled 28 km in 4 seconds, and then its speed increased by 3 km/s. We need to find the speed of the rocket at the end of the fifth second.

Solution

To solve this problem, we can break it down into two parts: 1. Calculate the initial speed of the rocket. 2. Calculate the speed of the rocket at the end of the fifth second.

Let's calculate the initial speed of the rocket first.

Calculating the Initial Speed

We are given that the rocket traveled 28 km in 4 seconds. To find the initial speed, we can use the formula:

Speed = Distance / Time

Substituting the given values, we have:

Initial Speed = 28 km / 4 sec

Converting the units to km/s:

Initial Speed = 7 km/s.

Now, let's calculate the speed of the rocket at the end of the fifth second.

Calculating the Speed at the End of the Fifth Second

We are given that the rocket's speed increased by 3 km/s. Since the speed is increasing uniformly, we can assume that the rocket's speed increases by the same amount every second.

To find the speed at the end of the fifth second, we can add the increase in speed to the initial speed for each second.

Speed at the end of the fifth second = Initial Speed + (Increase in speed per second * Number of seconds)

Substituting the given values, we have:

Speed at the end of the fifth second = 7 km/s + (3 km/s * 5 sec)

Calculating the result:

Speed at the end of the fifth second = 7 km/s + 15 km/s

Speed at the end of the fifth second = 22 km/s.

Therefore, the speed of the rocket at the end of the fifth second is 22 km/s.

Conclusion

The speed of the rocket at the end of the fifth second is 22 km/s.