A particle moves in a straight line so that, t seconds after passing through a fixed point O, its velocity, v ms⁻¹, is given by v = 3t² - 30t+72.
- (a)Find the distance between the particle's two positions of instantaneous rest.[6]
- (b)Find the acceleration of the particle when t = 2.[2]
Mark scheme
Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.
- (a) M1 Factorises or solves 3t²-30t+72=0 or t² -10t + 24 = 0
- (a) A1 t = 4, t = 6
- (a) M2 M1 for any two terms correct Integrates v to find F(t): 3t³/3 - 30t²/2 + 72t
- (a) M1 dep on at least M1 for integration Correct substitution for F(6) – F(4) or F(4) – F(6) FT their 4 and their 6 provided they are both positive
- (a) A1 dep on all previous marks being awarded 4 (m)
- (b) B1 [a=]6t-30
- (b) B1 [When t = 2: a = 6(2) – 30 =] -18 (ms⁻²) cao
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