Numerical Problems | Chapter 4 | Dynamics II | 9th Physics National Book Foundation | Federal Board

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Why long spanner is used to open or tight nuts of vehicle’s tyre? While tightening a small nut, extra-long wrench is not suitable. Why?
Why door knobs are fixed at the edge of door? What will happen it the door knob is at the middle of the door?
If you drop a feather and a bowling ball from the same height, which one will reach the terminal velocity first? Which one of them will hit the ground first?
Why do ice skates effortlessly slide on ice, while your shoes cause skidding?
Explain why it’s easier to push a car on flat tyres than inflated ones. What happens to the frictional force between the tyres and the road?
When standing on a crowded school bus, which stance would provide better stability and prevent you from being pushed over: legs joined or legs spread apart?
Why a moving bicycle is easier to balance? Relate this to the principles of rotational motion.
Why is a pencil standing on its tip unstable and what factors affect the stability of an object balanced on a point?
While driving what happens if the driver take the curve too fast? How does centripetal force play a role in keeping the car from skidding off the road?
Consider a situation where you swing a ball connected to a string in a circle. How does the tension in the string vary as the ball moves across different points in its circular path, and what forces are involved?
Why is it important for communication satellites in geostationary orbit to maintain a specific speed?
Calculate the torque acting on spanner of length 20cm to loosen a nut by a force of 50N. If the same nut is to be loosen up by force of 100N, what should be length of spanner?
A long uniform steel bar of length 1.0m is balanced by a pivot at its middle. Two mass m_1 and m_2 are suspended at a distance of 0.2m and 0.3m respectively from the pivot. Ignoring mass of the steel bar, if mass m_1=0.6kg find mass m_2.
Two masses, 250g and 100g are hanging at positions 65cm and 80cm, respectively, on a uniform meter rod, pivoted at 50cm mark as shown. Where should a third mass of 400g be positioned to balance the road?
A car weighing 1200kg enters a roundabout with a diameter of 60 meters at a speed of 25km/h. Calculate the centripetal force acting on the car as it navigates the curve.
A geostationary satellite revolves around earth in an orbit of radius 42000km. Find orbital speed of the satellite at this height.
4.1 A Physics teacher was explaining the role of moment arm in torque by performing an experiment. The teacher applied a force of 60N to open a door. The force is applied at three different points perpendicularly and their distances from the axis of rotation:
(a) 𝒅_𝑨=𝟎.𝟒𝟎𝒎, (b) 𝒅_𝑩=𝟎.𝟐𝟎𝒎 and (c) 𝒅_𝑪=𝟎.𝟎𝒎. Find the torque produced in each cases.
4.2 Kamil and Bilal are sitting on a seesaw at F9 Park Islamabad. Kamil, weighing 250N, is sitting at a distance of 0.6m from the pivot. At what distance from the pivot should Bilal, weighing 200N sit in order to balance the seesaw?
4.3 Bilal is performing in hammer throw game as shown in figure. Mass of the metal ball is 𝟓𝒌𝒈 and length of the string is 𝟏.𝟓𝒎. What centripetal force must Bilal apply to get a speed of 𝟐𝟓𝒎/𝒔?
4.4 Earth completes one revolution around the sun in 𝟑𝟔𝟓.𝟐𝟓 days. Find the orbital speed of Earth around the sun if it is 𝟏𝟓𝟎 million km away from the sun.