Conceptual Questions | Physics 9th Chapter 4 Turning Effect of Forces | KPK Textbook Board Peshawar

Описание: Q. Choose the best possible option.
(i) Conventionally anti clock wise torque is taken as
(a) Negative (b) Positive  (c) Parallel (d) Zero
(ii) A door requires a minimum torque of 80Nm in order to open it. What is the minimum distance of the handle from the hinges, if the door is to be pulled with a force at the handle not greater than 100N?
(a) 0.6m (b) 1m (c) 0.4m (d) 0.8m
(iii) Two children are balanced on opposite sides of a seesaw. If one child leans inward toward the pivot point, her side will
(a) rise (b) fall (c) insufficient data (d) neither rise nor fall
(iv) A body in equilibrium must not be
(a) at rest (b) moving (c) rotating (d) accelerating
(v) The torque in uniformly rotating fan having blade of length 0.5m is
(a) 0.5Nm (b) 2Nm (c) -0.5Nm (d) 0Nm
(vi) A force of 100N is applied perpendicularly at 0.5m, to turn of wheel of a bus. The torque acting on nut is
(a) 500Nm (b) 50Nm (c) 5Nm (d) 0.005Nm
(vii) The shortest distance between two couple forces is
(a) moment arm (b) couple arm (c) radius (d) double moment
(viii) A girl pushes to open a door perpendicularly with a force of 25N at 0.6m from the hinge, the torque is
(a) 41.6Nm (b) 25.6Nm (c) 15Nm (d) 0Nm
(ix) The angle at which x and y components of force are equal is
(a) 0 (b) 30 (c) 45 (d) 60
(x) CM is different from CG, when we have nonuniform
(a) shape of object (b) mass of object (c) gravitational force (d) none of these
Q. Give a short response to the following questions
(i) Can the rectangular components of the vector be greater than the vector itself? Explain.
(ii) Explain why door handles are not put near hinges?
(iii) Can a small force ever exert a greater torque than a larger force? Explain.
(iv) Why it is better to use a long spanner rather than a short one to loosen a rusty nut?
(v) The gravitational force acting on a satellite is always directed towards the centre of the earth. Does this force exert torque on satellite?
(vi) Can we have situations in which an object is not in equilibrium, even though the net force on it is zero? Give two examples.
(vii) Why do tightrope walkers carry a long, narrow rod?
(viii) Why does wearing high-heeled shoes sometimes cause lower back pain?
(ix) Why it is more difficult to lean backwards. Explain?
(x) Can a single force applied to a body change both its translational and rotational motion? Explain.
(xi) Two forces produce the same torque. Does it follow that they have the same magnitude? Explain.
(xii) Describe the path of the brick after toy suddenly let go of the rope.
Q. Solve the following numerical questions.
1. To open a door force of 15N is applied at 30o to the horizontal, find the horizontal and vertical component of force.
2. A bolt on a car engine needs to be tightened with a torque of 40Nm. You use a 25cm long wrench and pull on the end of the wrench perpendicularly. How much force do you have to exert?
3. Sana, whose mass is 43kg, sits 1.8m from the center of a seesaw. Faiz, whose mass is 52kg, wants to balance Sana. How far from the center of the seesaw should Faiz sit?
4. Two kids of weighting 300N and 350N are sitting at the ends of 6m long see-saw. The seesaw is pivoted at tis centre. Where would a third kid sit so that the see-saw is in equilibrium in the horizontal position? The weight of third kid is 250N. (ignore the weight of see-saw)
5. Two children push on opposite side of a door during play. Both push horizontally and perpendicular to the door. One child pushes with a force of 20N at a distance of 0.60m from the hinges, and the second child pushes at a distance of 0.50m. What force must the second child exert to keep the door from moving? Assume friction is negligible.
6. A construction crane lifts building material of mass 1500kg by moving its crane, calculate moment of force when moment arm is 20m. After lifting the crane arm, which reduces moment arm to 12m calculate moment.