Electric Force and Object Acceleration

[mli273]

1. An object with a charge of -2.9 microC and a mass of .012 kg experiences an upward electric force, due to a uniform electric field, equal in magnitude to its weight.

Part A: Find the magnitude of the electric field. Which I correctly calculated to be 4.1 x 10^4 N/C.

Part 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. F=ma



3. I'm not really sure how to calculate the acceleration of the problem. Any ideas?

 

[Doc Al]

What happens to the electric force if the charge is doubled? What happens to the net force on the object?

ΣF = ma

 

[mli273]

is the net force doubled as well?

 

[Doc Al]

is the net force doubled as well?

What was the net force originally?

 

[mli273]

Net force was F=mg so F=(.012)(9.81)= .11772 N

 

[fizzynoob]

you have two forces, gravity and the electric force due to the electric field.

You need to sum the all of the forces in your system (in the Y direction)

Electric Force = q*E

sum of the forces = 2qE - mg = ma; //solve for a

If the acceleration is greater in than gravity, than the direction is obviously ...

 

[mli273]

you have two forces, gravity and the electric force due to the electric field.

You need to sum the all of the forces in your system (in the Y direction)

Electric Force = q*E

sum of the forces = 2qE - mg = ma; //solve for a

If the acceleration is greater in than gravity, than the direction is obviously ...

Ok, well a = [2(-2.9x10^-6)(4.1x10^4) - (.012)(9.81)]/.012 = -29.6 m/s^2

But this is not the correct answer according to Mastering Physics.

 

[Doc Al]

Net force was F=mg so F=(.012)(9.81)= .11772 N

No, mg is just one of the forces on the object. What's the other? What's the net force?

Hint: To solve part B you won't need the result from part A.

 

[mli273]

No, mg is just one of the forces on the object. What's the other? What's the net force?

Hint: To solve part B you won't need the result from part A.

Oh..I get it. So it would be 2q -mg= ma, so the answer would be 9.81 m/s^2 & it's positive because the force is upward. Thank you so much!