11. A 1 kg box (mass) is dropped from a 10th story window. a. What is its acceleration? b. What for?

Question

11. A 1 kg box (mass) is dropped from a 10th story window.

a. What is its acceleration?

b. What force does it hit the ground with?

c. After the box hits the and stops moving A force of 10 N is used to move the 1 kg box forward what is the acceleration of the box?

d. What forces are acting opposite the 10 N force used to push the box forward?

Answer 1

Saying there is no resistance from air:

A. Falling due to gravity a=9.81 m/s

B. F = ma

     F = 1 kg * 9.81 m/s

     F = 9.81 N

C. F = ma

     10 N = 1 kg * a

     10 m/s = a

d. friction from the surface the box is sliding on

Answer 2

a. the accleration of gravity which is 9.8 m/s^2

b. the force of gravity which is mg = (1)(9.8) - 9.8 N

c. F = ma so 10 = (1)a which gives a = 10 m/s^2

d. The friction between the box and the ground. There are actually two frictional forces: one is static and the other is kinetc. The static one must be overcome to get gthe block moving and once it is moving the kinetic friction must be used. They both have the form:

F = cmg

Wher:

c = the coefficient of either static or kinetic friction

m = mass of object

g = acceleration of gravity