# Newton's Laws of Motion problem help

Hi everyone! Im really bad in physics so I need help in my assignments. My problem is what formula to use. Here's the problems.

## Homework Statement

An electron (mass = 9.11 x 10-31 kg) leaves one end of a tv picture tube with zero (0) initial speed and travels in a straight line to the accelerating grid, which is 1.80 cm away. It reaches the grid with a speed of 3.00 x 1006 m/s; If the accelerating force is constant, compute:
a.) acceleration
b.) time to reach the grid
c.) net force in Newtons (gravitational force on the electron may be neglected)

given:
m = 9.11 x 10-31
vo = 0 m/s
vF = 3.00 x 1006
d = 1.80 cm = 0.018m

In A:
I've thought of two formulas. Both give different results. These are:

a = v/t

Since there is no TIME, I will have to solve for time using:
t = m(v - vo) / F

The other formula I have thought of is:
a = v2 / 2x (from v2 = vo2 + 2ax)

In B:
It's either:
t = m(v - vo) / F
or
t = d/v

both giving different results again

In C:
It's obviously F = ma...

rl.bhat
Homework Helper
To calculate acceleration a, use v^2 = vo^2 + 2ax

To find t, use v = vo + at.

To calculate acceleration a, use v^2 = vo^2 + 2ax

To find t, use v = vo + at.

Thank you.
About solving for t, my teacher didn't give that kind of formula, is that a formula from Force?

Delta2
Homework Helper
Gold Member
Thank you.
About solving for t, my teacher didn't give that kind of formula, is that a formula from Force?

You already give a=v/t which is the same as v=v0+at for v0=0. This formula comes from the definition of acceleration a=dv/dt, if we know that a is constant .

oh ok thanks. ^^

rl.bhat
Homework Helper
Thank you.
About solving for t, my teacher didn't give that kind of formula, is that a formula from Force?

The formula for t is derived from the definition of the acceleration.