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Wonders of Physics


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Finding resultant force from 2 forces at 0 to 90 degree

Answer: Option A

Refer to the video tutorial for the explanation.

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Impressive Bugatti Chiron

This impressive Bugatti Chiron can accelerate from rest to 400 km/h and decelerate to a complete stop in merely 42 seconds! Our normal cars on the expressway travel about 90 km/h and the F1 race yesterday night is about 300 km/h. This Bugatti Chiron is faster than most bullet trains and comparable to the speed of a magnetic levitation train!

Capturehttps://www.bugatti.com/chiron

Before we look at the video, let’s do some calculations:

Capture2

Let’s find the acceleration of the car to reach 400 km/h in 32.6 sec:

Converting 400 km/h to m/s:    400km/1h = 400 000m/3600s =111 m/s

acceleration, a = (v – u)/t = (111 – 0) / 32.6 = 3.4 m/s2

hmmm…. this acceleration doesn’t seem impressive… it is way below free fall acceleration!

But we are not being fair here. To achieve the max speed of 400 km/h is not easy due to the resistive force (air resistance and friction) as speed increases. We should compare fairly the acceleration to reach 100 km/h instead like how we typically compare sports car like Ferrari etc.

Let’s find the acceleration of the car to reach 100 km/h (27.8 m/s) in 2.4 sec:

acceleration, a = (v – u)/t = (27.8 – 0) / 2.4 = 11.6 m/s2

This is greater than acceleration due to gravity (free fall) and much faster than most sports cars in the market like Ferrari or Lamborghini!

Now, let’s find the deceleration of the car when it slows down from 400 km/h to a complete stop in 41.9 – 32.6 = 9.36 s

acceleration, a = (v – u)/t = (0 – 111) / 9.36 = -11.9 m/s2

Take note of the spoiler being activated when it decelerates. This increases the drag (air resistance) to slow down the car, in addition to using the normal brakes. It is the same principle as the aeroplane when it lands and slows down on the runway.

 

 

 


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Vector Diagram – Parallelogram Method for 4 different kinds of questions

For Combined Science Physics Olevel, when constructing vector diagram, a method called Parallelogram Method is commonly used.

Parallelogram Method is used when 2 forces are known, and the resultant (net) force R, can be found.

Below show 5 different variations of questions when can be solved by using Parallelogram Method:

(A) Body has acceleration, forces are unbalanced, there is a resultant force R (Newton’s 2nd law)
(B) Body at rest, all forces are balanced, there is no resultant force R (Newton’s 1st law)
(C) Body moving at constant velocity, all forces are balanced, there is no resultant force (Newton’s 1st law)
(D) Finding unknown force (with resultant force R  + another known force are given)
(F) Vector diagram is applicable to all vector quantities (with magnitude and direction). Not just for forces.

Click here to view video tutorials on how to construct parallelogram step-by-step

Vector Diagram Parallelogram 01Vector Diagram Parallelogram 02Vector Diagram Parallelogram 03Vector Diagram Parallelogram 04

For Pure Physics, another method is the closed-loop triangle, where only 1 known force with 2 other unknown force. Click here to view the video tutorials.