CJC 2020 A level H2 Physics Answers

1 H2 Physics 9749 – 2020 A Level Exam Paper 1 1 Essential Question(s):  What is the relationship between V and r?  Which rule do we apply to determine percentage uncertainty for value obtained through multiplication/division? Solution: volume V = 4/3 r3 V / V = 3 r/r V / V x 100 % = = 3 r/r x 100% percentage uncertainty in volume = 3 percentage uncertainty in radius graph of percentage uncertainty in volume vs perc entage uncertainty in radius is a straight line graph passing through the origin with gradient = 3 Answer: B 2 Essential Question(s):  What are the four conditions that action-reaction force need to meet? Solution: The reaction force of the weight of the car is the gravitational force on the Earth by the car; the reaction force of the normal contact force on the car in the force on the ground by the car. Answer: D 3 Essential Question(s):  What is the unit of stress?  What is the unit of strain?  How do we determine the unit of a quantity represented as the area under a graph? Solution: stress= F/ A ; strain = e/L Units of stress = N m-2 Units of e = unit of L = m units of strain = unit of e / units of L = m / m strain has no unit units of area under stress-strain graph = units of stress x units of strain = N m-2 J = N m  N = J m-1 units of area under stress-strain graph = N m-2 = (J m-1) m-2 = J m-3 Answer: D

2 This question gave candidates a novel situation and asked them to use their knowledge of units to answer it. Those candidates who got this wrong tended to choose distractor C, probably because they confused newtons and joules. 4 Essential Question(s):  What does the area under the velocity – time graph represent? Solution: distance travelled by car X = P + Q + R distance travelled by car Y = S + Q + R Both cars were at the same position at t = 0, and again at t = T. Hence between t = 0 to t = T, both cars travelled the same distance. P + Q + R = S + Q + R P = S Answer: A 5 Essential Question(s):  What is relative velocity?  How do we determine the relative velocity on an object with respect to another? Solution: relative velocity of bicycle with respect to car vbc= vb– vc = vb + (- vc) vb = velocity of the bicycle vc = velocity of the car vbc = velocity of the bicycle relative to the car Answer: C Examiner’s comments: This was on relative velocities and proved dem anding with a significant number of candidates choosing distractor D, where the relative velocity of the bi cycle is shown pointing away from the car. 6 Essential Question(s):  What are the two conditions for a body to be in equilibrium? Solution: Option C is wrong because the direction of the torque is to be mentioned. The statement should be “The torque provided by the vertical forces is equal and opposite to the torque provided by the horizont