A spring is hung vertically from a fixed point. A mass M is hung from the other end of the spring, as illustrated in Fig. 3.1. The mass is displaced downwards and then released. The subsequent motion of the mass is simple harmonic. The variation with time t of the length L of the spring is shown in Fig. 3.2.
- (a)(i)State: one time at which the mass is moving with maximum speed time = ................................................................ s[1]
- (a)(ii)one time at which the spring has maximum elastic potential energy. time = ................................................................ s[1]
- (b)(i)Use data from Fig. 3.2 to determine, for the motion of the mass: the angular frequency ω ω = ............................................................ rad s⁻¹[2]
- (b)(ii)the maximum speed maximum speed = ............................................................ m s⁻¹[2]
- (b)(iii)the magnitude of the maximum acceleration. maximum acceleration = ............................................................ m s⁻²[2]
- (c)The mass M is now suspended from two springs, each identical to that in Fig. 3.1, as shown in Fig. 3.3. Suggest and explain the change, if any, in the period of oscillation of the mass. A numerical answer is not required.[2]
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Mark scheme
Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.
- 3(a)(i) 0.10s or 0.30s or 0.50s or 0.70s or 0.90 s A1
- 3(a)(ii) 0 or 0.40s or 0.80 s A1
- 3(b)(i) = 2π / Τ C1 = 2π / 0.40 = 16 rad s-1 A1
- 3(b)(ii) Vo = ωΧο C1 = 15.7 x 2.5 x 10-2 = 0.39 m s-1 A1 or tangent drawn at steepest part and working to show attempted calculation of gradient (C1) leading to vo = 0.39 m s¯¹ (allow ± 0.15 m s-1) (A1)
- 3(b)(iii) ao = ω²Χο C1 ao = (15.72 x 2.5 × 10-2) = 6.2 m s-2 A1 or ao = ωνο (C1) ao = 15.7 x 0.39 = 6.2 m s-2 (A1)
- 3(c) period is shorter/lower B1 Any one from: • greater spring constant/stiffness • (restoring) force is greater (for any given extension) • acceleration is greater (for any given extension) • greater energy/maximum speed (for a given amplitude) B1
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