Danny lowers the sails on his boat. he paddles upstream at 19 km/hr. the current is still running downstream at 15 km/hr. what is the actual velocity of the boat? 34 km/hr, downstream 34 km/hr, upstream 4 km/hr, downstream 4 km/hr, upstream

upstream 4 km/h

Explanation:

Let's define "upstream" as positive direction for the velocities. Therefore, we have:

is the velocity of Danny paddling, which is positive because it is upstream

is the velocity of the current, which is negative because it is downstream

Velocity is a vector, so we have to calculate the resultant velocity. However, the two velocities are along the same direction (just with opposite sign), so their resultant is given by their sum:

and the positive sign means the direction is upward.

it is a negative acceleration

force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

                                              ⇒      

here   k is the proportionality constant whose value is 1.

                                                            [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.