Question

стрела массой 20г. выпущена из лука вертикально вверх с начальной скоростью 20 м/с.Определите кинетическую энергию на высоте 15 м.

Answer 1

Eп. = mgh = 10*0.02*15 = 3Дж.

Eк. = mV^2/2 = 0.02*20^2/2 = 4Дж. 

4 - 3 = 1Дж.

Answer 2

Calculation of Kinetic Energy at Height 15m

To calculate the kinetic energy of the arrow at a height of 15m, we need to consider the conservation of mechanical energy. At the highest point of its trajectory, the arrow will have maximum potential energy and zero kinetic energy. As it falls from that point to a height of 15m, its potential energy will decrease, and an equal amount of kinetic energy will increase.

The formula for kinetic energy is:

Kinetic Energy (KE) = (1/2) * mass * velocity^2

Given: - Mass of the arrow (m) = 20g = 0.02kg - Initial velocity (v) = 20 m/s - Height (h) = 15m

To find the kinetic energy at a height of 15m, we need to calculate the velocity of the arrow at that height. We can use the principle of conservation of mechanical energy to do this.

At the highest point of the arrow's trajectory, all of its initial kinetic energy will be converted into potential energy. Therefore, we can equate the initial kinetic energy to the potential energy at a height of 15m:

Initial Kinetic Energy = Potential Energy at 15m

(1/2) * m * v^2 = m * g * h

Simplifying the equation:

(1/2) * v^2 = g * h

where g is the acceleration due to gravity (approximately 9.8 m/s^2).

Now, we can solve for the velocity (v) at a height of 15m:

v^2 = 2 * g * h

v = sqrt(2 * g * h)

Substituting the given values:

v = sqrt(2 * 9.8 * 15) ≈ 17.146 m/s

Now that we have the velocity at a height of 15m, we can calculate the kinetic energy using the formula mentioned earlier:

KE = (1/2) * m * v^2

KE = (1/2) * 0.02 * (17.146)^2 ≈ 2.33 Joules

Therefore, the kinetic energy of the arrow at a height of 15m is approximately 2.33 Joules.

Please note that the above calculation assumes no air resistance and neglects any other external forces acting on the arrow during its flight.

Conclusion

The kinetic energy of the arrow at a height of 15m is approximately 2.33 Joules.