Thursday, April 14, 2011


question 1

A lorry haning a mass of 1.5t is travel-ling along a level road at 72 km/h. when the brakes are applied, the speed decreases to 18 km/h. determine how much the kinetic enegy of the lorry is reduced.

Initial velocity of lorry, v1                  = 72 km/h

                                       km                    m            1h
                            =  72   −−−   x  1000     −−−    x    −−−
                                        H                     km         3600s

                               =  −−−   = 20 m/s

Final velocity of lorry, v2                =  18
                                                        −−−  =   5 m/s and

Mass of lorry , m                             = 1.5t = 1500 kg

Initial kinetic energy of the lorry        1                    1
                                                  = −−− mv ²   =   −−−  (1500)(20) ²
                                                      2          ¹        2                   
             = 300 kj

Final kinetic energy of the lorry         1                  1
                                                 =  −−  mv²  =   −− ( 1500)(5) ²
                                                      2     ²           2
 = 18.75 kj

Hence, the change in kinetic energy    = 300 – 18.75
                                                        = 281.25 kj


A rod of mass  M=3KG  and length  L=1.2m  pivots about an axis, perpendicular to its length, which passes through one of its ends. What is the moment of inertia of the rod? Given that the rod's instantaneous angular velocity is  60deg/s  what is its rotational kinetic energy?

Answer: The moment of inertia of a rod of mass M and length L about an axis, perpendicular to its length, which passes through its midpoint is I = (1/12)ML². This is a standard result. Using the parallel axis theorem, the moment of inertia about a parallel axis passing through one of the ends of the rod is

I¹ I + M ( L / 2) ²=1/3 ML²

I¹ = 3 x 1.2² =1.44 kg m²
The instantaneous angular velocity of the rod is 

w = 60 x  π  = 1.047 rad/s

Hence, the rod's rotational kinetic energy is written 

K = 1 I¹ w² = 0.5 x 1.44 x 1.047² = 0.789 J

Wednesday, March 16, 2011


Question 1.

How does the movement of the earth affects the distribution of solar energy in the earth's surface?


These two phenomena of circulation of the earth and the earth's rotation on its 
axis is the variation of solar influence on the earth surface. he earth's rotation 
axis tilt of the angle 231 / 2 degrees is causing the phenomenon of day and 
night occur. Earth takes 24 hours to make one complete rotation. The Earth 
rotates west to east. The surface of the earth facing the sun during the day and 
would have received a lot of solar energy distribution compared with that
 experienced on earth during the night.

                            Question 2.

How rotation engine work?


Rotation engine is a type of internal combustion engines that use design to change
 the rotation of the pressure of combustion air-fuelmixture directly to the rotational motion,
 unlike ordinary piston engine which produces a reciprocating motion before
 being transferred to the rotational movement of the crankshaft. In the four-stroke cycle
 engine generated in the space between the housing shaped like oval epitrokoid
 the triangular rotor. This design produces a smooth high-rpm power from a compact
 and lightweight engine.

Sunday, January 30, 2011



1) Amirul Akhmar B Mohd Sabri

2) Mohammad Anuar Fitri B Sahimi

3) Mohammad Shafiqal Bin Mat Saad

4) Mohammad Syafiq Fitri Bin Shaarani