I need some serious help with my physics!!!!?

Question

A box weighing 70 N rests on a table. A rope tied to the box runs vertically upward over a pulley and a weight is hung from the other end (Fig. 4-37).

Determine the force that the table exerts on the box if the weight hanging on the other side of the pulley weighs:

(a) 27 N

(b) 65 N

(c) 104 N

Answer 1

Fig. 4-37?
Interesting...

The table must exert a force (N) equal to the force the box exerts upon it.
Let Wb- weight of the box
W= weight on the other side of the pulley
then
N=Wb - W

N= 70 - W

a) N= 70 - 27= 43
b) N= 70 - 65 = 5
c) N= 70 - 104=0 ('cause the 70N weight is in the air)

Answer 2

The pulley tranfers the force of the weight around to the box.
In other words the tension in the rope is equal to the weight of weight.

The table exerts a force equal to that pushing down on it by the box. If the rope is pulling up on the box with 27 N then the 70 N box is only pushing down on the table with 43N.
there for the force exerted by the table equals 43N.

a) 70 N - 27 N = 43 N

b) 70 N - 65 N = 5 N

c) 70 N - 104 N = -34 N (so the box would accelerate off the table)

Answer 3

1.) Create a free body diagram with all forces (with corresponding directions and points of application).

2.) Since the box is at rest and not accelerating, you know that the sum of all forces in all directions must equal zero.

3.) Do your own homework.