Forces, Movement, Shape, and Momentum

A uniform beam is 3.0 m long and weighs 120 N. It is supported horizontally at its two ends, P and Q. A load of 90 N is placed 2.0 m from end P.

Explain the meaning of the term 'pivot' in the context of turning effects of forces.

A uniform plank of wood is 4.0 m long and has a weight of 200 N. It rests horizontally on two supports placed 0.5 m from each end.

Explain why it is easier to loosen a tight bolt using a spanner with a long handle rather than a short one.

A mechanic uses a wrench to loosen a bolt. The wrench is 0.30 m long, and he applies a force of 150 N perpendicular to the wrench at its end.

State what is meant by the 'centre of gravity' of a body, and describe how the weight of a body acts with respect to this point.

A uniform horizontal rod of length 1.8 m and weight 90 N is supported at its two ends, labelled P and Q. A load of 60 N is hung from the rod, 0.3 m from end P.

Look at the table showing different forces applied to a door at various distances and angles from the hinge (pivot).

A bridge is supported at both ends. A heavy truck stops near the left end of the bridge. Explain, using the principle of moments, how the upward forces at the left and right supports change as the truck moves from the left end to the centre of the bridge.

A uniform metal plank of length 2.5 m and mass 4.0 kg is placed horizontally across a small stream, resting on rocks at each end (points R and S). A stone of mass 2.0 kg is placed 0.75 m from end R, as shown.

Take gravitational field strength . Ignore the weight of the plank unless stated otherwise.