Intermediate Level

5 Worksheet

acceleration of free fall g = 9.81 m s−2

Intermediate level

1Define the moment of a force.[1]

2State two conditions that must be met for the equilibrium of an extended object.[2]

3The diagram shows the downward forces applied on a plastic ruler.

Deduce whether or not the ruler is in equilibrium.[3]

4A person of weight 820 N stands on one leg. The area of the foot in contact with the floor is 1.4×10−2 m2.

aCalculate the pressure exerted by the foot on the ground.[2]

bExplain what would happen to the pressure exerted on the floor if the person stands on
tiptoe onone leg. [1]

5Define thetorque of a couple, and give one example of a couple.[2]

6The diagram shows a uniform beam of length 1.5m and weight 60N resting horizontally on two supports. /

aBy taking moments about the support A, determine the force RB at the supportB.[3]

bUse your answer to a to calculate theforce RA at support A.[1]

Higher level

7A ladder of mass 32 kg rests at an angle against a
smooth wall as shown in the diagram.
The centre of gravity of the ladder is at its midpoint.
aDetermine the force R exerted by the wall on theladderby taking moments about the base
of the ladder.[3]
bExplain why the force at the base of the ladder wasnotincluded when doing the calculation in a. [1] /

8A 62kg person lies flat on a uniform plank of mass 15kg. The plank, with the person lying on it, is placed on a brick and some bathroom scales, as shown in the diagram below.

The person’s toe-to-head distance is 1.56m. The length of the plank is also 1.56m.

aSketch the diagram above. On your sketch, show all the forces acting on the plank.[2]

bThe reading on the bathroom scales is 30kg. Use this information to determine how far thecentre of gravity of the person is from the toes. [4]

9A flagpole of mass 25 kg is held in a
horizontal position by a cable as shown
in the diagram.
The centre of gravity of the flagpole is at
a distance of1.5 m from the fixed end. Determine:
athe tension T in the cable[4]
bthe vertical component of the force at
the fixed end of the pole.[2] /
Extension
10The diagram shows a wheel of mass 20 kg
and radius 80 cm pulled by a horizontal
force F against a step of height 20 cm.
Determine the magnitude of the initial
force Fso that the wheel just turns over
the step.[4] /
11A metal rod of length 90 cm has a disc of radius 24 cm fixed rigidly at its centre, as shown in the diagram. The assembly is
pivoted at its centre.
Two forces, each of magnitude 30N, are applied normal to the rod at each end so
as to produce a turning effect on the rod.
A rope is attached to the edge of the disc to prevent rotation. Calculate the minimum tension Tin the rope. [4] /

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