A radioactive substance has a decay probability of λ = 0.0025 s-1. How long will it take for the activity to drop to 20 % of its present value?

Cells in the nervous system have a potential difference of 70 mv across the cell membrane separating the interior of the cell from the extracellular fluid. this potential difference is maintained by ion pumps that move charged ions across the membrane. is this an emf? select the correct answer and explanation. 1)no. the ion pumps cannot separate charges; thus, they cannot create a potential difference. 2)yes. the ion pumps cannot separate charges, but they still can create a potential difference. 3)yes. the ion pumps can actively separate charge; thus, they can create a potential difference. 4)no. the ion pumps can separate charges, but they cannot create a potential difference.

A60-kg box is being pushed a distance of 6.8 m across the floor by a force p with arrow whose magnitude is 162 n. the force p with arrow is parallel to the displacement of the box. the coefficient of kinetic friction is 0.24. determine the work done on the box by each of the four forces that act on the box. be sure to include the proper plus or minus sign for the work done by each force. (the floor is level and horizontal. forces that act on the box: pushing force p, frictional force f, normal force n, and weight mg.)

Which force would exist in a free body diagram of this car accelerating along the highway?