Physics homework -- guy runs 28.5m in 11.5s,

• daniel20152015
In summary, the question asks for the average velocity of a person who runs 28.5m in 11.5s, waits 45s, and then runs back to the starting point in 22s. The answer is zero as displacement is zero. The concept of average velocity is based on displacement and time, whereas average speed is based on total distance and time.
daniel20152015

Homework Statement

I have a problem where a guy runs 28.5m in 11.5s, waits 45s, then runs back to the starting point in 22s. What's the average velocity?

The Attempt at a Solution

Would it be zero because the displacement is zero or would I calculate the 57 total meters ran divided by the overall time?

Welcome to PF!

What is the definition of average velocity? Its based on displacement and time so what is it?

daniel20152015 said:
Would it be zero because the displacement is zero or would I calculate the 57 total meters ran divided by the overall time?

Hi Daniel! Welcome to physics forum!:)
The question asks to find the average velocity not average speed. Your answer is correct. As displacement is zero so average velocity is zero. But average speed is not zero.

1. How do you calculate the speed of the guy running?

The speed of an object can be calculated by dividing the distance it travels by the time it takes. In this case, the speed of the guy running would be 28.5 meters divided by 11.5 seconds, which equals 2.48 meters per second.

2. Can you convert the speed to miles per hour?

Yes, to convert meters per second to miles per hour, you can use the conversion factor of 2.237. Therefore, the speed of the guy running would be approximately 5.56 miles per hour.

3. What is the acceleration of the guy running?

Acceleration is the rate of change of an object's velocity. To calculate it, you would need the initial velocity, final velocity, and the time it took to change from the initial to the final velocity. As we only have the distance and time, we can calculate the average acceleration using the formula: acceleration = (final velocity - initial velocity) / time. In this case, the initial velocity can be assumed to be 0, so the acceleration would be 2.48 m/s divided by 11.5 seconds, which equals 0.215 m/s².

4. How much work did the guy do while running?

Work is defined as the force applied to an object multiplied by the distance it moves in the direction of the force. In this case, we would need to know the force the guy exerted while running. As we do not have this information, we cannot calculate the amount of work done.

5. Can you determine the guy's kinetic energy after running?

Kinetic energy is the energy an object possesses due to its motion. It is calculated using the formula: KE = 1/2 * mass * velocity². As we do not have the mass of the guy, we cannot determine his kinetic energy after running.

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