CHAPTER 12. FORCE,MOMENTUM AND IMPULSE 12.3
- What force T at an angle of 30◦above the horizontal, isrequired to drag a blockweighing 20
N to the right at constant speed, if the coefficient of kinetic friction between the block and the
surface is 0,20?
- A block weighing 20N rests on a horizontalsurface. The coefficientof static friction between
the block and the surface is 0,40 and the coefficient of dynamic frictionis 0,20.
(a) What is the magnitude of the frictional forceexerted on the block while the block is at rest?
(b) What will the magnitude of the frictional force be if a horizontal force of 5 N is exerted on
the block?
(c) What is the minimumforce required to start the block moving?
(d) What is the minimum force required to keepthe block in motion once it has been started?
(e) If the horizontal force is 10 N, determine thefrictional force.
- A stationary block ofmass 3kg is on top of aplane inclined at 35 ◦to the horizontal.
35 ◦
3kg
(a) Draw a force diagram(not to scale). Include the weight of the block aswell as the compo-
nents of the weight thatare perpendicular and parallel to the inclined plane.
(b) Determine the values of the weight’s perpendicular and parallel components.
(c) There exists a frictional force between the block and plane. Determine this force (magni-
tude and direction).
- A lady injured her back when she slipped and fell in a supermarket.She holds the owner ofthe
supermarket accountable for her medical expenses. The owner claimsthat the floor covering
was not wet and meetsthe accepted standards.He therefore cannot accept responsibility. The
matter eventually endsup in court. Before passing judgement, the judge approaches you, a
science student, to determine whether the coefficient of static friction ofthe floor is a minimum
of 0,5 as required. Heprovides you with a tilefrom the floor, as well as one of the shoes the
lady was wearing on theday of the incident.
(a) Write down an expression for the coefficientof static friction.
(b) Plan an investigationthat you will perform toassist the judge in his judgement. Follow the
steps outlined below toensure that your plan meets the requirements.
i. Formulate an investigation question.
ii. Apparatus: List all the other apparatus, except the tile and the shoe, that you will need.
iii. A stepwise method:How will you performthe investigation? Include a relevant, la-
belled free body-diagram.
iv. Results: What will you record?
v. Conclusion: How will you interpret the results to draw a conclusion?
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(1.) 01w3 (2.) 01w4 (3.) 01w5 (4.) 01w6 (5.) 01w7 (6.) 01w8
