# Physics Homework

**I need all answers worked out showing how i got the answer**

**1-** Two forces, one equal to 15 N and another equal to 40 N, act on a

50-kg crate resting on a horizontal surface as shown in the accompa-

nying figure.

(a) What is the net horizontal force on the crate?

(b) What is its horizontal acceleration?

(c) If the crate starts from rest, what is its horizontal speed after 5 s?

(d) How far has the crate traveled along the surface in this time?

**2-** As a horse and wagon are accelerating from rest, the horse exerts a

force of 400 N on the wagon ( ● Figure 2.53). Illustrating Newton’s

third law, the wagon exerts an equal and opposite force of 400 N.

Because the two forces are in opposite directions, why don’t they

cancel each other and produce zero acceleration (i.e., no motion)?

**3-** Perhaps you’ve noticed that the rockets used to put satellites and

spacecraft into orbit are usually launched from pads near the equa-

tor. Why is this so? Is the fact that rockets are usually launched to

the east also important? Why?

**4-**A 200-kg communications satellite is placed into a circular orbit

around Earth with a radius of 4.23 107 m (26,300 miles)

(see ● Figure 2.54).

(a) Find the gravitational force on the satellite. (There is some useful

information in Section 2.8.)

(b) Use the equation for centripetal force to compute the speed of

the satellite.

(c) Show that the period of the satellite—the time it takes to com-

plete one orbit—is 1 day. (The distance it travels during one orbit

is 2 p, or 6.28, times the radius.) This is a geosynchronous orbit:

the satellite stays above a fixed point on Earth’s equator