A particle of mass 1.3 kg rests on a rough plane inclined at an angle θ to the horizontal, where tan θ = 12/5. The coefficient of friction between the particle and the plane is μ.
- (i)A force of magnitude 20 N parallel to a line of greatest slope of the plane is applied to the particle and the particle is on the point of moving up the plane. Show that μ = 1.6.[4]
- (ii)The force of magnitude 20 N is now removed. Find the acceleration of the particle.[2]
- (iii)Find the work done against friction during the first 2 s of motion.[3]
Mark scheme
Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.
- [B1] Resolve forces perpendicular to plane. Allow 67.4 used
- [B1] Resolve forces parallel to plane. Allow 67.4 used
- [M1] Use F = μR
- [A1] AG Must be from exact working here
- [M1] For applying Newton's second law along the plane and also using F = μR (3 terms)
- [A1] a = 3.08 ms⁻²
- [M1] Use s = ut + ½at² with u = 0 and their a ≠ g to find the distance moved in the first 2 seconds
- [M1] WD = F × d
- [A1] WD = 49.2 J
- Alternative method for question 4(iii)
- [M1] Finding v after 2 seconds and using WD = PE loss – KE gain
- [M1] (Implicitly covers s = ut + ½at² and WD=Fd as intermediate steps in PE/KE calculations)
- [A1] WD = 49.2 J
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