Fores in action

The diagram shows an object submerged in water. The object is stationary in the water. Which statement about the upthrust acting on the object is correct?

A It is zero.

B It is equal to the weight of the object.

C It is equal to the mass of the object.

D It is equal to the volume of the water displaced.

B

The diagram shows two opposite vertical forces acting on an object. Which of the following statements could be correct?

1 The object is accelerating and moving up.

2 The object is decelerating and moving down.

3 The magnitude of the resultant force is 0.9 N.

A Only 3

B Only 1 and 3

C Only 2 and 3

D 1, 2 and 3

D

The diagram shows a uniform rod at rest in a horizontal position. The rod is hinged at point X. A cable is attached to a vertical wall and the midpoint of the rod. Which arrow best represents the direction of the force on the rod at point X?

C

A cylinder of wood is placed in water. The density of the wood is 6.0×10² kgm^–3. The density of water is 1.0×10³ kgm^–3.

What fraction of the volume of the cylinder is below the water line?

A 0.6

B 0.4

C 0.2

D 1.0

A

The diagram shows a crane lifting a car. The crane has a working efficiency of 60%. Suggest and explain two ways the crane can be modified to improve its efficiency.

• Suggestion to reduce heat losses through friction in moving parts e.g. oil, bearings

• Use a stiffer / stronger cable to reduce energy loss through stretching