An 85 kg football player traveling 4.7 m/s is stopped in 1.0 s by a tackler. What is the original kinetic energy of the player? (I tried using 1/2 m v^2 but that doesn't seem to be right. How do I manipulate the formula?) What average power is required to stop him?
It is right, 1/2 m v^2 is the original KE.
average power= energy/timestopping
50 joules
934 joules
To calculate the original kinetic energy of the football player, you can indeed use the formula you mentioned: KE = 1/2 * m * v^2. It seems that you might not be getting the correct answer due to not adjusting the velocity correctly. Let me explain the calculations step by step:
1. Given values:
- Mass of the player (m) = 85 kg
- Initial velocity of the player (v) = 4.7 m/s
2. Calculate the original kinetic energy:
- KE = 1/2 * m * v^2
- Substituting the values:
KE = 1/2 * (85 kg) * (4.7 m/s)^2
KE = 1/2 * 85 kg * 22.09 m^2/s^2
KE = 941.825 J (rounded to three decimal places)
Therefore, the original kinetic energy of the player is approximately 941.825 Joules.
Now let's move on to calculating the average power required to stop the player.
Average power is defined as the amount of work done per unit time. In this case, the work done is equal to the change in kinetic energy of the player.
3. Calculate the change in kinetic energy:
- Change in KE = Final KE - Initial KE
- Since the player is stopped, the Final KE = 0 J
- Change in KE = 0 J - 941.825 J
- Change in KE = -941.825 J (negative value because the kinetic energy decreases)
4. Calculate the average power:
- Power = Work / Time
- Since power is the average power required to stop the player, it can be calculated as:
Power = Change in KE / Time
Power = -941.825 J / 1.0 s
Power = -941.825 W (rounded to three decimal places)
It's important to note that the negative sign indicates that the average power required to stop the player is being exerted in the opposite direction of the player's motion.