F = (1.6 × 10−19 C)(3 N/C) = 4.8 × 10−19 N
Because the electron has a negative charge, the force is opposite the electric field, or right.
(b) Even though we’re dealing with an electric force, we can still use Newton’s second law. Since the
electric force is the only force acting, just set this force equal to ma and solve. The direction of the
acceleration must be in the same direction as the net force.
4.8 × 10−19 N = (9.1 × 10−31 kg)a
a = 2.8 × 10^8 m/s^2 , leftInclined Planes
How to Do It
Use the following steps to solve these kinds of problems: 1) Draw a free-body diagram for the object (the
normal force is perpendicular to the plane; the friction force acts along the plane, opposite the velocity);
2) break vectors into components, where the parallel component of weight is mg (sin θ ); 3) write
Newton’s second law for parallel and perpendicular components; and 4) solve the equations for whatever
the problem asks for.
Don’t forget, the normal force is NOT equal to mg when a block is on an incline!
The Drill
Directions: For each of the following situations, determine:
(a) the acceleration of the block down the plane
(b) the time for the block to slide to the bottom of the planeIn each case, assume a frictionless plane unless otherwise stated; assume the block is released from rest
unless otherwise stated.
1 .