I'm on the AQA January 2013 Unit 4 paper now, I've not had much trouble with most of the question but hoping someone can help with these three which I couldn't do...
9. Two pendulums, P and Q, are set up alongside each other. The period of P is 1.90 s andthe period of Q is 1.95 s. How many oscillations are made by pendulum Q between two consecutive instantswhen P and Q move in phase with each other?
A 19
B 38
C 39
D 78
12. The gravitational field strength at the surface of the Earth is 6 times its value at thesurface of the Moon. The mean density of the Moon is 0.6 times the mean density ofthe Earth. What is the value of the ratio ?
A 1.8
B 3.6
C 6.0
D 10
13. The diagram shows two points, P and Q, at distances r and 2r from the centre of aplanet. The gravitational potential at P is –16 kJ kg–1. What is the work done on a 10 kg masswhen it is taken from P to Q?
A – 120 kJ
B – 80 kJ
C + 80 kJ
D + 120 kJ