Acceleration Topic Assessment Answers: --- Integral Variable

(a) Find ( v(t) ) (3 marks) (b) Find ( s(t) ) (2 marks) A car starts from rest with acceleration [ a(t) = 3t - \frac{t^2}{2} ]

(b) ( s(t) = \int (8t^{3/2} - 54) dt = 8 \cdot \frac{2}{5} t^{5/2} - 54t + D = \frac{16}{5} t^{5/2} - 54t + D ) ( s(4) = \frac{16}{5} \cdot 32 - 216 + D = \frac{512}{5} - 216 + D = 20 ) ( \frac{512}{5} - 216 = \frac{512}{5} - \frac{1080}{5} = -\frac{568}{5} ) So ( -\frac{568}{5} + D = 20 \Rightarrow D = 20 + \frac{568}{5} = \frac{100}{5} + \frac{568}{5} = \frac{668}{5} ) [ s(t) = \frac{16}{5}t^{5/2} - 54t + \frac{668}{5} ] (a) ( v(t) = \int \left(3t - \frac{t^2}{2}\right) dt = \frac{3t^2}{2} - \frac{t^3}{6} + C ) Starts from rest: ( v(0) = 0 \Rightarrow C = 0 ) [ v(t) = \frac{3t^2}{2} - \frac{t^3}{6} ] --- Integral Variable Acceleration Topic Assessment Answers

(c) Check if ( v(t) = 0 ) in [1,4]: ( v(t) = 4t^3 - 4t^2 + 2t + 3 ) Test ( t=1 ): ( 4 - 4 + 2 + 3 = 5 >0 ) Test ( t=0 ): ( 3 >0 ), cubic positive, likely no root. Check derivative: ( 12t^2-8t+2>0 ) (discriminant 64-96<0) so ( v(t) ) increasing, always positive. No change of direction. (a) Find ( v(t) ) (3 marks) (b)

(b) ( v(t) = 0 \Rightarrow \frac{t^2}{2}\left(3 - \frac{t}{3}\right) = 0 ) ( t = 0 ) or ( t = 9 ) seconds (answer: ( t = 9 )) (b) ( v(t) = 0 \Rightarrow \frac{t^2}{2}\left(3 -

(a) Find the velocity function ( v(t) ) (2 marks) (b) Find the time when the car is momentarily at rest again (2 marks) (c) Find the distance travelled up to that time (1 mark) A particle’s acceleration is given by [ a(t) = 2\cos(2t) - \sin t ] At ( t = 0 ), ( v = 1 ), ( s = 0 ).

(c) ( s(t) = \int v(t) dt = \frac{t^3}{2} - \frac{t^4}{24} + D ), ( s(0) = 0 \Rightarrow D = 0 ) Distance ( = s(9) = \frac{729}{2} - \frac{6561}{24} ) ( = 364.5 - 273.375 = 91.125 \ \text{m} ) (or ( \frac{729}{8} \ \text{m} )) (a) ( v(t) = \int (2\cos 2t - \sin t) dt = \sin 2t + \cos t + C ) ( v(0) = 0 + 1 + C = 1 \Rightarrow C = 0 ) [ v(t) = \sin 2t + \cos t ]

(a) Find ( v(t) ) (3 marks) (b) Find ( s(t) ) (3 marks) (c) Calculate the total distance travelled between ( t = 1 ) and ( t = 4 ) seconds, explaining how you treat any change of direction. (3 marks) Q1 (a) ( v(t) = \int (6t - 4), dt = 3t^2 - 4t + C ) ( v(0) = 5 \Rightarrow C = 5 ) [ v(t) = 3t^2 - 4t + 5 ]