Prefixes are used to simplify the writing of very big or very small numbers. For instance, instead of having to write 12 500 000 m every time, you can simplify it by using the prefix mega (M), hence it can also be written as 12.5 Mm. Similarly, 0.00054 s can be written as 0.54 ms. If you are unsure or confused with the unit conversions, you can refer to the following videos. 1) Prefixes can be used for different physical quantities units. 2) Unit conversion with examples 3) Unit conversion for units of area and volume 4) Unit conversion for units of speed and density

Answer: Option C Focal length f is the distance between the focal point and the centre of the lens (optical centre) . Note that only when parallel rays of light enter a converging lens, the rays will converge to a point. That point is considered to be focal point F (principal focus). The distance between focal point F and the optical centre is the focal length f. Refer to below. As none of the options is similar to the above definition, you have to consider that the rays from a distant (far away) object are considered parallel . Hence the sharp image formed on the screen is considered the forcal point F of the lens and the distance between the image and the optical centre is the focal length f. If it is a close object, the rays entering are not considered parallel. Hence even if the rays converged to a point, that point is NOT focal point F and the distance between this converged point and the optical centre is NOT focal length f.

When gas in piston and heated but pressure remains constant. It is easier to explain in terms of the average force acting on a unit area. 2008PPp1q15 Answer: B 2017PPp1q15 Answer: A In short:  Temperature increases , Kinetic Energy increases , Rate of Collision decreases , Collision force on wall increases (due to higher speed), Average force per unit area remains constant , Pressure constant . As piston is free to move, it will move to the right such that the pressure remains constant (equal to atmospheric pressure outside). As the piston moves to the right, the volume inside the piston increases .  Surface area of piston in which the air molecules collide increases . The rate of collision decreases as the number of molecules remains constant. With higher KE of molecules, the molecules will collide the wall with greater force . Though rate of collision decreases, with each collision having greater impact force, this makes average force per unit area acting on the wall of piston remains the same. Hence pressure remains constant. Misconception : Many think that the rate of collision remains the same, which is wrong . Considering per unit area, if rate of collision remains the same, with the speed of the molecules increases, there will be greater collision force with the wall. This will result in the average force per unit area being higher, hence the pressure would increase.  If the rate of collision increased , with the speed of the molecules increases, there will be greater collision force with the wall. This will result in the average force per unit area being much higher, hence the pressure would increase even more.

When a system is in equilibrium , 2 conditions are met. 1) Principle of Moment (POM): Sum of anticlockwise moment = Sum of clockwise moment 2) Net force = 0N; all forces are balanced: Total downward forces = Total upward forces Whenever a force passed through the pivot point, that force will not create any moment as there is no perpendicular distance from the force to the pivot. Hence this force will not be included in the calculation of moments.

Jet Suit Flight and Talk by Richard Browning Setting Records Real Ironman Another kind of jet suit by another company

In this post, it shows a free-falling ball from a height of 1.0 m. During the impact, the direction of the force on the ground is downwards and the force on the ground by the ball is greater then the weight. As the ball is free-falling, the only force acting is its weight downwards. Hence a common misconception is to think that the force on the ground during impact is equal to the weight. This is wrong. The normal force (force on the ball by the ground = stopping force on the ball by the ground) is greater than the weight . The force on the ball by the ground is equal and opposite to the force on the ground by the ball . Hence the magnitude of the force on the ground is greater than the weight . Similar concept can be applied if a man jumps off from a height. But in this case, the man’s leg will exert a stopping force over a short distance. That stopping force, once again, is greater than the weight of the man.