How much work is required to stop an electron (m = 9.11 10-31 kg) which is moving with a speed of 1.99 106 m/s?

It is equal to the kinetic energy of the electron.

how do you find the kinetic energy though?

0.5*mass*velocity squared

I tried that but the answer I came up with was incorrect... Are you sure that's the right way to solve this?

the kinetic energy on e- is negative

To determine the work required to stop an electron, we need to calculate the kinetic energy (KE) of the electron and then convert it to work.

The kinetic energy of an object can be calculated using the formula:

KE = 1/2 * mv^2

Where:
KE is the kinetic energy
m is the mass of the object
v is the velocity of the object

Given:
m = 9.11 * 10^-31 kg (mass of the electron)
v = 1.99 * 10^6 m/s (velocity of the electron)

Substituting the given values into the formula, we have:

KE = 1/2 * (9.11 * 10^-31) * (1.99 * 10^6)^2

Now, let's calculate the kinetic energy:

KE = 0.5 * (9.11 * 10^-31) * (1.99 * 10^6)^2

KE = 0.5 * (9.11 * 10^-31) * (3.96 * 10^12)

KE = 0.5 * (9.11 * 3.96) * 10^-19

KE = 18.068 * 10^-19

KE = 1.8068 * 10^-18 Joules

Now that we have the kinetic energy, we know that work (W) is equal to the change in kinetic energy. Since we want to stop the electron, its final kinetic energy would be zero. Therefore, the work required is equal to the initial kinetic energy:

W = 1.8068 * 10^-18 Joules

Thus, the amount of work required to stop the electron is 1.8068 * 10^-18 Joules.