# Grade 12 Physics (South African curriculum – physical science paper 1) – Assignment

**QUESTION 1**

A helicopter is flying vertically up at an unknown constant velocity. An object is dropped from the helicopter when it is exactly 88 m above the ground. The object takes 1.5 s to reach its maximum height from the time it was released. Air friction is ignored.

1.1) Calculate the magnitude of the velocity of the object at the point of release. (3)

1.2) Calculate the maximum height, above the ground, reached by the object. (4)

1.3) Calculate the velocity of the object the instant it hits the ground. (4)

1.4) Using the ground as the zero position, and taking upward as the positive direction, sketch a position-time graph for the object from the time it is released to the time it hits the ground. (4)

QUESTION 2

A man skis down a 50 m snow slope which makes an angle of 20º with the horizontal. The total mass of the skier and skis is 80 kg. A constant frictional force of 50 N acts on the skis as the skier moves down the slope. The speed of the skier at the top of the slope is 5 m·s^{–1}.

2.1 Draw a free body diagram showing all the forces acting on the skier as he skis down the incline. (3)

2.2 Use the work-energy theorem to calculate the speed of the skier at the bottom of the slope.

QUESTION 3

The diagram shows two trolleys, A of mass 0.2 kg and B of mass 0.4 kg, moving to the left at 3 m·s^{–1}. The trolleys are attached by a compressed spring. The spring is released and immediately after this trolley A moves to the left at 4 m·s^{–1}.

3.1) State the principle of conservation of linear momentum. (3)

3.2) Calculate the velocity of trolley B immediately after the spring is released. (5)

3.3) Is the above collision elastic or inelastic? Perform a calculation to justify your answer. (5)

QUESTION 4

New cars have a crumple zone to help minimize injuries during accidents. In addition to seat belts, airbags and padded interiors can reduce the chance of death or serious injury.

4.1 Use principles in Physics to explain how airbags can reduce the chance of death or injury. (3)

4.2 In a crash test, a car of mass 1.2 × 103 kg collides with a wall and rebounds as illustrated below. The initial and final velocities of the car are 12 m·s^{–1} to the left and 2 m·s^{–1} to the right respectively. The collision lasts 0.1 s.

4.2.1 Impulse of the car during the accident. (4)

4.2.2 Average force exerted on the car. (3)