Plugging in values

Using

Using

Combining equations

Plugging in values:

Kinetic energy is equal to . The object of mass  and velocity  therefore has kinetic energy equal to . Let's let the object of mass  have velocity . Therefore, its kinetic energy is . We want to find  such that the two objects to have the same kinetic energy, so we can equate their two kinetic energies. 

The equation for kinetic energy is:

, where  is the velocity of the object. Therefore, if we halve the velocity, we can substitute that into our equation, and see what will change in the kinetic energy equation:

Thus, the kinetic energy is quartered.

To answer this question, we'll need to use the formula for kinetic energy.

Plugging in the values given to us, we can solve for our answer.

The equation for kinetic energy is:

Where  is the object's kinetic energy,  is the object's, and  is the object's velocity.

We can see that the relationship between kinetic energy and mass is linear, so when the velocity is doubled, the kinetic energy is also doubled.

The equation for kinetic energy is:

Where  is the object's kinetic energy,  is the object's, and  is the object's velocity.

We can see that the relationship between kinetic energy and velocity is quadratic, so when the velocity is doubled, the kinetic energy is quadrupled.

Find the final velocity by multiplying the average velocity by 2. Then substitute into the equation for kinetic energy.

This problem can either be very simple or very complex.

You could convert the contractor's potential energy into kinetic energy, and then find the velocity at which he hits the seesaw. Then, use that to calculate the kinetic energy of the bricks and the height at which the bricks will fly. Although some may find that fun to do, it's unnecessary.

If we assume that all of the energy of the man is transferred to the bricks, we can use the conservation of energy equation:

We need to make a few clarifying statements for our initial and final states. In the initial state, the contractor is at a height of 1.5m and not moving. The bricks are not moving at this point either. In the final state, the man is on the ground not moving, and the bricks are at a height of 10m and not moving. Therefore, we can rewrite the above equation as the following:

Rearranging for the mass of the bricks:

Using the equation for conservation of energy, we get:

Let's clarify that our initital state is when the ball is at its maximum height and the final state is when it reaches the ground. Plugging in our expressions and removing initial kinetic and final potential energy, we get:

Note that we removed initial kinetic energy despite the ball moving. At the initial state, all of the ball's velocity is horizontal. Since there is no vertical velocity, we can ignore it for now, coming back to it later.

We multiply the initial energy by 0.85 because the problem statement says that we lose 15% of the ball's total energy after hitting the rim. Rearranging for final velocity:

This is only the y-component of the final velocity. We need to combine this with the x-component to get the total velocity. The problem statement tells us that the final horizontal velocity is , therefore we can write: