The line of tension by charge

By winding the long cylindrical solenoid of radius R takes a constant current, which creates a uniform inside the solenoid magnetic field of B. In the solenoid coils of it flies in the radial (perpendicular
axis of the solenoid), the electron velocity v (see Figure). Deviating in a magnetic field, the electron after some time left solenoid. Determine the time T of the electron motion inside the solenoid.

throwing the ball

The roof height H from a distance L from a man wants to throw the ball (see Figure). What is the minimum value of the initial velocity of the ball for a throw?

Find the acceleration of the cube. No friction.