# Given mass, distance, and time, calculate power

• MathMajor
In summary, the conversation is about determining the amount of power a weightlifter expends when lifting a 50kg barbell a distance of 1.2m in a time interval of 1.5s. The correct equation for power is Fd/t, and when plugged in with the given values, the answer is 392 Watts. The student was initially told by their professor that the correct answer is 40 Watts, but after further discussion, it was agreed that the student's answer was actually correct.
MathMajor

## Homework Statement

How much power does a weightlifter expend when lifting a 50kg barbell a distance of 1.2m in a time interval of 1.5s?

## Homework Equations

Power=work done/time interval (in Newton meters per second or Watts)
Work=Fd (in Newton meters or Joules)

## The Attempt at a Solution

Power = Fd/t = (m)(a)(d)/t = 50kg(9.8 m/s2)(1.2m)/1.5s = 392 Nm/s = 392 W

This is how I solved the problem, but my professor said the correct answer is 40 Watts!
Work = force x distance; work = 50 kg x 1.2 m, work = 60
Power = work /time; 60/1.5 = 40 Watt

Can someone please verify which way is correct? I am sticking by my answer of 392 Watts

MathMajor said:

## The Attempt at a Solution

Power = Fd/t = (m)(a)(d)/t = 50kg(9.8 m/s2)(1.2m)/1.5s = 392 Nm/s = 392 W

This is how I solved the problem, but my professor said the correct answer is 40 Watts!
Work = force x distance; work = 50 kg x 1.2 m, work = 60
Power = work /time; 60/1.5 = 40 Watt

'50kg' is a mass and not a force, it must be correctly multiplied by acceleration (gravity in this case) to convert it to a force. You are correct.

Ok, so you are sure the correct answer is 392 Watts? I feel like I will be shunned for going against the professor, but I have to go with my gut on this one.

Thanks!

MathMajor said:
Ok, so you are sure the correct answer is 392 Watts? I feel like I will be shunned for going against the professor, but I have to go with my gut on this one.

Thanks!

I didn't check over your answer, but I am quite sure that 'kg' is a unit of mass and not force.

I agree. Thanks!

## 1. What is power?

Power is the rate at which work is done or energy is transferred. It is measured in units of watts (W) or joules per second (J/s).

## 2. How do you calculate power?

Power is calculated by dividing the work or energy (measured in joules) by the time (measured in seconds). The formula for calculating power is: power = work / time.

## 3. What is the relationship between mass, distance, time, and power?

The relationship between mass, distance, time, and power is described by the formula for power. Mass and distance do not directly affect power, but they may indirectly affect the work or energy involved, which in turn affects power. Time is the determining factor in the calculation of power.

## 4. Can power be negative?

Yes, power can be negative. This occurs when work is being done on an object instead of by an object. In this case, energy is being transferred into the object, resulting in a negative value for power.

## 5. What are some real-life examples of power calculations?

Power calculations are commonly used in various fields such as physics, engineering, and sports. Some examples include calculating the power output of a car engine, determining the power needed to lift an object using a crane, or calculating the power output of an athlete during a race.

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