PHYSICS CLASS 9th
Numerical problems
MOTION
Notions :
we denote physical quantities by a special and unique symbol to avoid confusion.
time t ;
speed v ; and veocity v;
acceleration a;
initial velocity u;
final velocit v ;
average speed w ;
average velocity w ;
radius of circle r;
angular displacement θ ;
angular velocity ω ;
IMPORTANT FORMULA :
Distance travelled = speed × time or s = v × tDisplacement = velocity × time or s = v × t
Average speed = ( total distance travelled ) ÷ ( total time taken)
Average velocity = ( initial velocity + final velocity ) ÷ 2 or w = (u + v) ÷ 2
Acceleration = ( Change in velocity ) ÷ ( time taken ) or
= ( final velocity - initial velocity ) ÷ time taken or a = ( v – u ) ÷ 2
Linear velocity = angular velocity × radius of the circle.
Equations of Motion : 1) v = u + at
2) s = ut + 1/2 at²
3) v² = u² + 2as
Now solving some problems based on motions
Q 1) A car traveles 30 km at a uniform speed of 40 km/h and the next 30 km at a uniform speed of 20 km/h. Find its average speed.
Q 2) Rahim driving his motorbicycle and go to office. He computes the average speed for the trip to be 20 km/h . on the return trip along the same route, there is less traffic and the average speed is 40 km/h. What is the average speed for Rahim’s total trip?
Q 3) On a 120 km track, the train travels first 30 km at uniform sped of 30 km/h. How fast must the train travel the next 90 km so as to average speed 60 km/h for the entire trip ?
Q 4) A ball hits a wall horizontally at 6.0 m/s. It rebounds horizontally at 4.4 m/s. The ball is in contact with the wall for 0.040 s. What is the acceleration of the ball ?
Q 5) A car travels 100 km at aspeed of 60 km/h and return with speed of 40 km/h. Calculate the average speed for the whole journey.
Q 6) convert a speed of 72 km/h into
(a) m/s
(b) cm/s.
Q 7) suppose you walk across a room of length 9 m with a velocity of one and half kilometre per hour. Express this velocity in unit of m/s and find the time you will take to move across the room.
Q 8) An electric train is moving with a velocity of 120 km/h. How much distance will it move in 30 s ?
Q 9) A car is traveling at 54 km/h
If it's velocity increases to 72 km/h in 5 s , then find the acceleration of the car in SI units
Q 10) A racing car has a uniform acceleration of 5 m/s². What distance will it cover in 20 s after starting from rest?
Q 11) A bullet is fired on a wall with a velocity of 100 m/s. If the bullet stops at a depth of 10 cm inside the wall, then find the retardation produced by the wall.
Q 12) find the initial velocity of car which is stopped in 10 seconds by applying breaks. Retardation due to breaks is 2.5 m/s².
Q 13) an object udergoses an acceleration of 10 m/s² starting from rest. Find the distance traveled in 5 seconds.
Q 14). An artificial satellite takes 90 minutes to complete it's revolution around the earth. Calculate the angular speed of the satellite.
Q 15) Calculate the angular speed of the second's hand of a clock, assuming that it moves with a uniform angular speed. If the length of second's hand is 2 cm, calculate the speed of tip of the second's hand.
Answers
- 26.6 km/h
- 26.7 km/h
- 90 km/h
- -260 m/s
- 48 km/h
- (a) 20 m/s
7. 21.4 s
8. 1 km
9. 1m/s²
10. 1000 m ( 1 km ) in 20 seconds
11. Retardation produced by the wall = 50000 m/s²
12. u = 25 m/s.
13. s = 125 m
14. 0.0011 rad/s
15. 0.21 cm/s
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