Uniform Electric Field Upward Electric Force Equals Weight. HELP


by m_physics
Tags: w=mg electric field
m_physics
m_physics is offline
#1
Jan23-09, 12:58 AM
P: 7
1. An object with a charge of -3.6uC and a mass of .012kg experiences an upward electric force, due to a uniform electric field, equal in magnitude to its weight. (a) Find the direction and magnitude of the electric field. (b) If the electric charge on the object is doubled while its mass remains the same, find the direction and magnitude of its acceleration.



2. E=kQ/r(sqrd)
k=8.99 x 10^9 N*m^2/C^2
magnitude of electron's charge (e): 1.60 x 10 ^ -19 C




3. Attempt
W=mg
W= (.012kg)(10)
W=.12N

Upward force equal to magnitude in weight so...
W= W=kQ/r(sqrd)
.12N + (8.99 x 10^9) [(-3.6uC)(1.6 x 10^-19])/(r^2)
Solve for r
r=-431.52

Plug r into E equation to find electric charge.
E=kQ/r(sqrd)
E=(8.99 x 10^9) [(-3.6uC)(1.6 x 10^-9)]/(-431.52^2)
E= -51.7824/-431.52^2
E= -2.78 x 10 ^ -4

I have no idea about part b. Is it always equal to gravity? Is that how they found the answer.

Correct answer from book:
a) (-3.3 x 10^4 N/C) y direction
b) (9.81 m/s^2) y direction
Phys.Org News Partner Science news on Phys.org
NASA's space station Robonaut finally getting legs
Free the seed: OSSI nurtures growing plants without patent barriers
Going nuts? Turkey looks to pistachios to heat new eco-city
rl.bhat
rl.bhat is offline
#2
Jan23-09, 01:08 AM
HW Helper
P: 4,442
In the electric field force on a charge is equal to E*q
Hence mg = E*q. Now solve for E.


Register to reply

Related Discussions
Net Electric Field Equals Zero Introductory Physics Homework 1
Uniform Electric Field Introductory Physics Homework 16
electric potential in a uniform electric field...please help Introductory Physics Homework 1
Calculating Electric Potential in A Uniform Electric Field Introductory Physics Homework 4
Electric charge and fields: uniform electric field Introductory Physics Homework 1