CAIE
Physics
(9702)
Questions & Answers
Table 1.1 lists some physical quantities. Identify with ticks (✓) which quantities are vectors and which are scalars. Table 1.1 quantity scalar vector acceleration displacement gravitational potential energy speed temperature
A constant resultant force F acts on a car of mass m. The car moves from rest with constant acceleration a along horizontal ground. When the car has displacement s, the speed of the car is v. Using the concept of work done on the car, show that the kinetic energy EK of the car is given by the equation EK = 1/2 mv^2.
The mass of the car is 920 kg. At time t = 0, the car is at rest. At time t = 5.8 s, its velocity is 17 m s−1. Calculate the kinetic energy of the car at time t = 5.8 s.
Between time t = 0 and time t = 5.8 s, the work done against resistive forces is 4.7 × 10^4 J. Determine the average output power of the car during this time.
At time t = 5.8 s, the speed of the car becomes constant. State and explain whether the output power of the car is greater than, less than or the same as the output power just before t = 5.8 s.
Define the moment of a force about a point.
A tree of mass 270 kg grows out of sloping ground and is supported by a post, as shown in Fig. 2.1. The ground applies a total force R on the tree at point Q. The centre of gravity of the tree is a horizontal distance of 1.2 m from Q. The post applies a force F of 1800 N perpendicular to the line PQ. The line of action of F passes through point P at an angle θ to the vertical. P is a horizontal distance of 1.6 m from Q. The tree is in equilibrium and all forces act on the tree in the same plane. By taking moments about point Q, show that θ is 25°.
On Fig. 2.2, draw a labelled scale vector triangle to represent the forces acting on the tree. The weight of the tree has been drawn to scale.
The tree exerts a pressure of 150 kPa on the top of the post. Determine the surface area of the tree in contact with the post.
Two progressive water waves X and Y travel along a straight line from point A to point B. The variation of displacement of the waves with distance from A at an instant in time is shown in Fig. 3.1. State the amplitude of wave X.
Both waves have frequency 16 Hz. Determine the speed of wave X.
State and explain whether X and Y are coherent.
Wave X and wave Y superpose to form a resultant wave. On Fig. 3.2, sketch the variation of displacement of the resultant wave with distance from A at the instant of time shown in Fig. 3.1.
The intensity of wave X is IX. The intensity of wave Y is IY. Use Fig. 3.1 to determine the ratio IX/IY.
A small ball is dropped from rest from height h1 above the ground and falls vertically downwards. The ball collides with the ground and bounces back vertically upwards, reaching a maximum height h2. Fig. 4.1 shows the ball just before and just after hitting the ground. State and explain whether the collision is elastic or inelastic.
Calculate the change in momentum of the ball during the collision with the ground.
Determine the average force on the ball during the collision with the ground.
Calculate the ratio h2/h1.
Define the Young modulus.
A wire of unstretched length 0.81 m is made of a metal with Young modulus 95 GPa. The wire obeys Hooke's law and has a constant cross-sectional area. Fig. 5.1 shows the force-extension graph for the wire. Determine the cross-sectional area of the wire.
The extension of the wire is initially 2.0 × 10^-3 m. Determine the work done to increase the extension of the wire to 3.0 × 10^-3 m.
Define electric potential difference across a component.
A circuit contains four resistors and a battery of electromotive force (e.m.f.) 8.0 V with negligible internal resistance. When the variable resistor has resistance R, the currents in the circuit are 0.030 A, I1 and I2, as shown in Fig. 6.1. Determine the charge passing through the battery in a time of 4.0 minutes.
Calculate I1.
Calculate I2.
Determine R.
The variable resistor in (b) is fitted with a scale so that its resistance can be accurately determined. The resistor of resistance 240 Ω is now replaced by a new resistor X of unknown resistance. A galvanometer is connected as shown in Fig. 6.2. With reference to ratios of resistances, explain how this circuit can be used to determine the resistance of X.