The acceleration of an object in free fall motion is the constant acceleration due to gravity
(i) The gradient of the rocket at point <em>B</em> is approximately<u> -9.81 m/s²</u>
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(ii) The reason why the gradient is -9.81 m/s² is as follows;
The given graph is the speed to time graph with the upward direction taken as positive
- Gradient of the speed to time graph is the acceleration
Given that at point B the object is at the maximum point, the upward motion due to the rocket stops, the motion of the rocket is then due to gravity
Therefore, the gradient at <em>B</em>, is given as follows;
- Force = Mass × Acceleration
At point <em>B</em> the only force acting on the rocket is the force of gravity, therefore, the acceleration of the rocket at <em>B</em>, a = g, acceleration due to gravity ≈ 9.81 m/s², and the rocket is falling due to its weight
- Force acting at B = Weight = Mass × Acceleration due to gravity, g
Therefore, only gravitational force is acting on the rocket when the direction of the rocket changes and rocket falls freely, at <em>B</em>, and the acceleration of the rocket at <em>B</em> = g = 9.81 m/s²
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