Question

A charge of -50 uC is fixed in place. From a horizontal distance of 20 cm a particle of mas 7.20e-3 kg and charge - 40.0 uC is fired with an initial spped of 200.0 m/s directly toward the fixed charge. How far does the particle travel before its speed it zero?

Answer 1

Since both the charges are negative hence will repel each other initially. Then the repelling force on 2nd charge due to 1st charge is

where r= distance between charged particles= 20cm=0.2m

then using all the given and known values in SI units in above, we'll get

  

  

Then using Newton's Laws of motion,

where m= mass of 2nd charged particle= 7.20 * 10^-3 kg

a= acceleration

or

Now for the motion of 2nd charge,

Acceleration of motion, (It will be negative since 1st charge opposes the 2nd charge hence it lowers the speed of the 2nd particle)

Initial speed, u= 200 m/s

Final speed, v=0m/s

then let the distance travelled be "S", then using equations of motion,

  (ANS)