Everything Science Grade 11

12.3 CHAPTER 12. FORCE,MOMENTUM AND IMPULSE

(c) Measure the exact distance the rocket travelled. Calculate the average speed at

which the balloon travelled. To do this, dividethe distance travelled bythe time

the balloon was “in flight.” Fill in your results forTrial 1 in the Table below.

(d) Each team should conduct two more races and complete the sections in the Table

for Trials 2 and 3. Thencalculate the average speed for the three trials todetermine

your team’s race entry time.

Results:

Distance (m) Time (s) Speed (m·s−^1 )

Trial 1

Trial 2

Trial 3

Average:

Conclusions: The winner of this raceis the team with the fastest average balloon speed.

While doing the experiment, you should think about,

1. What made your rocket move?


2. How is Newton’s Third Law of Motion demonstrated by this activity?


3. Draw pictures usinglabelled arrows to showthe forces acting on theinside of the balloon before
   it was released and afterit was released.

Exercise 12 - 3

1. A fly hits the front windscreen of a moving car. Compared to the magnitude of the force thefly
   exerts on the windscreen, the magnitude of theforce the windscreen exerts on the fly during the
   collision, is:

(a) zero.

(b) smaller, but not zero.

(c) bigger.

(d) the same.

2. Which of the following pairs of forces correctly illustrates Newton’s Third Law?

A man standing still A crate moving at

constant speed

a bird flying at a con-

stant height and velocity

A book pushed

against a wall

�

force of floor

weight of man

on man

Force used to push

the crate

frictional force exerted

by the floor

� �

The weight of the bird =

force of Earth on bird

Weight of the bird

Force of wall on book Force of book on wall

A B C D

More practice video solutions or help at http://www.everythingscience.co.za

(1.) 01w1 (2.) 01w2