#4 #6 #16 #20 #22 4. A sky diver is being pulled down by the earth with a force of 970 N. If there is also an air resistance of 380 N, what additional force would be needed to maintain a constant speed?
Constant speed means there is no acceleration. A zero acceleration is the result of a zero net force. Our skydiver experiences a net force,
The force needed to counter this is 590 N UP.
6. What is the acceleration of a 500 kg buffalo if the net force on the buffalo is 2000 N?
We are given the force and the mass, so we solve the force equation for acceleration and insert the given values as shown below.
The units may not look like those associated with acceleration, but they are as we see in the units analysis below.
![4 N/kg = 4 (N/kg) {[(kg*m)/(s*s)]/N} = 4 m/s/s. Write it out in fraction form and cancel units appearing in both the numerator and deminator.](images/ch2x06b.gif)
16. A three kg ball has been thrown vertically upward. If we ignore the air resistance, what are the direction and size of each force acting on the ball while it is traveling upward?
The only force on the ball is gravity acting DOWN to the ground. We compute the weight of the ball as
20. A crate has a mass of 21 kg. What applied force is required to produce an acceleration of 3 m/s/s if the frictional force is known to be 90 N?
The net force is given via the product of the crate's mass and its acceleration.
Since we now know the net force and the frictional force, we are ready to determine the applied force.
We use the skydiver's acceleration and mass to find the net force.
With both the weight and net force in hand, we can find the force of air resistance acting on the skydiver.
