Answer:
≅3666.67 N
Explanation:
Use Newton's 2nd law, F = ma where F=force applied, m = mass of the object,
a = acceleration acquired by the object.
a= (v-u)/t where v = final velocity, u = initial velocity and t = time taken
calculate a = (30-0)/9 ≅ 3.33 m/s2
Then F = 1100×a = 3666.67 N
Answer:
D) the second at the doorknob
Explanation:
The torque exerted by a force is given by:

where
F is the magnitude of the force
d is the distance between the point of application of the force and the centre of rotation
is the angle between the direction of the force and d
In this problem, we have:
- Two forces of equal magnitude F
- Both forces are perpendicular to the door, so 
- The first force is exerted at the midpoint of the door, while the 2nd force is applied at the doorknob. This means that d is the larger for the 2nd force
--> therefore, the 2nd force exerts a greater torque