# OAT physics Ques need help

#### HOPEOPT

10+ Year Member
Hi every body I struggle solving theses problems in physics, theses questions are found in one of Kaplan practice exams but I could not find the solution:
1. Four point charges are arrangened in a line at the distances shown below. Charges A, B,C,D have magnetitudes of +9, -5C, -12C, respectively. A negative test charge is placed at point C.
A---------25cm-----B--------25cm----C-----25cm-----D.
What is the magnitude of the force acting on the test charge?. (K is Coulomb's constant, Z is the magnitude of the test charge in coulombs).
The answer is 236 kZ newtons
How we solve it?.

2.
A solid weights 60 ibs in air. To determine its density it is immersed in a test liquid of weight-density 10ibs/ft^3. If the solid weight 40 Ibs when immersed inthe liquid, its density is closest to :

how we solve it/.

#### KHE

##### Senior Member
15+ Year Member
Hi every body I struggle solving theses problems in physics, theses questions are found in one of Kaplan practice exams but I could not find the solution:
1. Four point charges are arrangened in a line at the distances shown below. Charges A, B,C,D have magnetitudes of +9, -5C, -12C, respectively. A negative test charge is placed at point C.
A---------25cm-----B--------25cm----C-----25cm-----D.
What is the magnitude of the force acting on the test charge?. (K is Coulomb's constant, Z is the magnitude of the test charge in coulombs).
The answer is 236 kZ newtons
How we solve it?.

2.
A solid weights 60 ibs in air. To determine its density it is immersed in a test liquid of weight-density 10ibs/ft^3. If the solid weight 40 Ibs when immersed inthe liquid, its density is closest to :

how we solve it/.

I was thinking about the questions you pose, and the fact that you and many others on here are taking or will have to take the OAT and I'm left with one thought....

BETTER YOU THAN ME!!!!!!!!!!!

#### sportsdude00

10+ Year Member
Hi every body I struggle solving theses problems in physics, theses questions are found in one of Kaplan practice exams but I could not find the solution:
1. Four point charges are arrangened in a line at the distances shown below. Charges A, B,C,D have magnetitudes of +9, -5C, -12C, respectively. A negative test charge is placed at point C.
A---------25cm-----B--------25cm----C-----25cm-----D.
What is the magnitude of the force acting on the test charge?. (K is Coulomb's constant, Z is the magnitude of the test charge in coulombs).
The answer is 236 kZ newtons
How we solve it?.

2.
A solid weights 60 ibs in air. To determine its density it is immersed in a test liquid of weight-density 10ibs/ft^3. If the solid weight 40 Ibs when immersed inthe liquid, its density is closest to :

how we solve it/.

1 is found by summing the forces from each individual charge. force is found using F=qE, with E being the electric field from a point charge (look up the formula), and q being the charge of the test charge. pay attention to the directions of the forces as well, as they act in different directions depending on the locations. you'll end up with something like Fnet=F(A)+F(B)-F(D). note that E depends on 1/r^2, so A will have a smaller contribution than B and D.

#### HOPEOPT

10+ Year Member
1 is found by summing the forces from each individual charge. force is found using F=qE, with E being the electric field from a point charge (look up the formula), and q being the charge of the test charge. pay attention to the directions of the forces as well, as they act in different directions depending on the locations. you'll end up with something like Fnet=F(A)+F(B)-F(D). note that E depends on 1/r^2, so A will have a smaller contribution than B and D.
Thank you very much