Question

A particle of mass 10-3 kg and charge 5 microC is thrown at a speed 20 m/s against a uniform electric filed of strength 2*105 N/C. How much distance will it travel before coming to rest momentarily?

Answer 1

mass of particle , m = 10⁻³ Kg
Charge on particle , Q = 5μC = 5 × 10⁻⁶C
Intial speed of of particle , u = 20 m/s
Strength of electric field , E = 2 × 10⁵ N/C
Particle is throwing with speed 20m/s against a uniform electric field
Means , F = qE
F = ma [ Newton's 2nd law ]
ma = qE
10⁻³ × a = 5 × 10⁻⁶ × 2 × 10⁵
a = 10³ m/s²
Because , particle is thrown against of electric field
Means a = - 10³ m/s² [ negative sign shows motion is regarding in electric field ]
Now, use formula
v² = u² + 2aS
When body will be rest , v = 0
0 = (20)² - 2 × 10³S
400 = 2000S
S = 0.2 m