Everything Science Grade 11

12.3 CHAPTER 12. FORCE,MOMENTUM AND IMPULSE

SOLUTION

Step 1 : Draw a force diagram

Draw a force diagram indicating all the horizontal forces on the system as a

whole:

2500 kg 10 000 N

T

Figure 12.5: Force diagram for truck pulling a trailer

Step 2 : Find the acceleration of the system

In the absence of friction, the only force that causes the system to accelerate is

the thrust of the engine.If we now apply Newton’s Second Law:

FR = ma

10000 = (500 + 2000)a

a = 4m· s−^2 to the right

Step 3 : Find the horizontal component of T

We are asked to find thetension in the tow bar, but because the tow bar is acting

at an angle, we need tofind the horizontal component first. We will find the

horizontal component in terms of T and thenuse it in the next step to find T.

T

T cos25◦

25 ◦

The horizontal component is T cos 25◦.

Step 4 : Find the tension in thetow bar

To find T, we will applyNewton’s Second Law:

FR = ma

F− T cos 25◦ = ma

10000 − T cos 25◦ = (2000)(4)

T cos 25◦ = 2000

T = 2206,76N

Object on an inclined plane

When we place an object on a slope the force of gravity (Fg) acts straight down andnot perpendicular
to the slope. Due to gravity pulling straight down, the object will tend toslide down the slope with a