Level 7
27. (a) A ladder is hung on one hook so that it balances horizontally.
Draw an arrow on the diagram below to show the position of the hook.
1 mark
(b) A window cleaner puts the ladder on his shoulder in the position shown.
(i) The weight of the ladder acts at its centre, as shown. Calculate the turning effect, or moment, about his shoulder due to the weight of the ladder. Give the unit.
.
2 marks
The window cleaner hooks his bucket onto the ladder as shown in the diagram. The bucket weighs 15 N and is 0.8 m from his shoulder.
(ii) Calculate the turning effect, or moment, about his shoulder due to the weight of the bucket only.
(iii) Calculate the size and direction (clockwise or anticlockwise) of the total turning effect, or moment, about his shoulder due to the weight of the ladder and the weight of the bucket.
(c) To keep the ladder and bucket balanced on his shoulder, the window cleaner has to pull down with his hand.
(i) How can he move the ladder on his shoulder to reduce the force his hand has to balance?
(ii) How could he change the position of the bucket to reduce the force his hand has to balance?
28. On a clear night, a camera was set up on a fixed stand pointing at the Pole Star. The camera shutter was opened and kept open for a number of hours. The diagram shows the paths of a number of stars appearing in the photograph.
(a) (i) In the photograph, most of the stars appear as curved lines instead of dots. Why do the stars appear as curved lines?
(ii) The Pole Star appears as a bright dot in the middle, not as a curved line. Why does the Pole Star appear as a dot?
(b) Study the diagram carefully. For how long was the camera shutter kept open?
. hours
29. A drawing pin is pressed into a notice board.
The pin is pressed into the notice board with a force of 20 N. The head of the drawing pin has an area of 100 mm2. The point of the pin has an area of 0.1 mm2.
(a) What is the size of the force exerted by the point of the pin on the notice board?
N
(b) Calculate the pressure exerted by the point of the drawing pin. Give the unit.
30. Two mirrors at 90° to each other always reflect a ray of light back parallel to the incident ray.
(a) (i) In the diagram below, a ray of light strikes mirror 1 at an angle of 45°.
Complete the diagram to show how the mirrors reflect the ray. Use a ruler and a protractor.
(ii) In the next diagram, a ray of light strikes mirror 1 at a different angle.
(b) Bicycles must have a reflector fixed to the rear mudguard or to the seat.
The diagram shows part of a bicycle reflector and an incident ray of light. The light passes through the flat surface and is reflected from the small ‘mirrors’.
(i) In which direction is the ray of light reflected?
(ii) At night, car drivers can easily see bicycle reflectors in the beam from their headlights. Explain why.
(iii) Why is a plane mirror not suitable as a bicycle reflector?
31. Regulus is a bright star in the constellation Leo. In February, an astronomer visited a country close to the equator. While she was there she observed Regulus.
(a) During the night, Regulus appeared to move across the sky.
(i) Why do stars appear to move across the sky?
(ii) Choose from the words below to complete the sentence.
north east south west
Regulus appeared to move across the sky from
north east south west to north east south west
(b) The diagram below shows the position of the Earth and the Sun when the astronomer made her observations. She noticed that Regulus was directly overhead at midnight. On the diagram, draw an arrow from the Earth to show the direction in which she looked to see Regulus.
(c) Six months later, in August, Regulus cannot be seen at any time.
Explain why.