Newton's second law states that force is a mass times an acceleration.

Assuming that all the original values were equal to 

We can substitute in new values for a doubled force and quadrupled mass to find the new acceleration.

This shows that the new acceleration will be  of the original value or equal to a/2.

Newton's second law states that force is a mass times an acceleration.

In order for a force to exist, there must be an acceleration applied to a mass. A force cannot exist on a massless object, nor can it exist without a net acceleration.

Newton's third law states that for every force on an object, there is an equal and opposite force from the object. These forces frequently cancel out, however, and produce a net force of zero.

To solve this problem we need to divide up the situation into two parts.  During the first part the person is jumping from the roof of a house and is therefore undergoing freefall and accelerated motion due to the force of gravity.  Therefore we will need to use kinematic equations to solve for the final velocity as the person lands.  In the second part of the problem, the person decelerates their torso through a specific distance and comes to a stop.  We will then need to calculate the acceleration of the torso during this second part to determine the average force applied.

Let us start with kinematics to determine the speed of the torso as it hits the ground.

Knowns

We can use the kinematic equation

This is the velocity of the torso as it hits the ground.  We will know use the same equation with new variables to determine the acceleration of the torso as it comes to a stop.

Knowns

Rearrange to get the acceleration by itself

We can now plug this into Newton’s 2nd Law to find the average force acting on the object.

Newton's second law allows us to solve for the force of gravity on the ball:

Newton's third law tells us that the force of the ball on the table, due to gravity, will be equal and opposite to the normal force of the table on the ball.

Substitute the equation for force of gravity.

Now we can use the mass of the ball and the acceleration of gravity to solve for the normal force. First, convert the mass to kilograms. Then, use the equation to find the normal force.

To determine this we would first need to determine the vertical component of the  force acting on the car.  To do this we would use the sine trigonometric function.

The pull in the vertical direction must be at least  to pull the car.  However, we also know there is another equal force on the tree on the other side of the pull.  Therefore the total pull must be double this value in order to pull both the tree and the car equally.