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Questions & Answers

"A car of mass 1500kg is travelling at 10 ms-1 along a horizontal road. A brake force of 3000N brings it to rest. Calculate the deceleration of the car and the distance travelled by the car whilst decelerating."

This is a classic forces question, which is seen in different variations throughout the past papers. To calculate the answer we will need to re-arrange the force equation: F=ma. 
Remember, here the F stands for the resultant force, m for mass and a for acceleration. 
To calculation the deceleration we will make “a” the subject: a=F/m. When we substitute the values we get, a= 3000/1500. The answer is -2ms-2. Since deceleration is equal to negative acceleration, the answer will be 2ms-2
To calculate the distance, we will use the equations of motion. Initial velocity, u =10 ms-1, final velocity, “v”= 0ms-1, because the car comes to rest. The acceleration “a”= -2ms-2. We need to calculate the distance “s”. We will use this equation: 2as=v^2-u^2. Make s the subject of the formula, it would become s=(v^2-u^2)/2a. Substitute the values and you will get your answer: (10^2)/2*-2 = 25m.

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