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NCERT Solutions for Class 9 Science Chapter 10
Class 9 science – Physics -Gravitation – Answers
Extra Questions with answers for practice
- Question 1:
A particular is dropped from a tower 180 m high. How long does it take to reach the ground? What is the velocity when it touches the ground? Take g = 10 m/s².
- Answer 1:
6 s, 60 m/s
- Question 2:
How much would a 70 kg man weigh on moon? What will be his miss mass on earth and moon? Given g on moon = 1∙7 m/s².
- Answer 2:
119 N, 70 kg, 70 kg
- Question 3:
A car falls off a ledge and drops to the ground in 0.5 s. Let g = 10 m/s² (for simplifying the calculations).
(a) What is its speed on striking the ground?
(b) What is its average speed during 0.5 s?
(c) How high is the ledge from the ground?
- Answer 3:
(a) 5 m/s (b) 2.5 m/s (c) 1.25 m
- Question 4:
Calculate the value of acceleration due to gravity on Moon. Give n mass of moon = 7.4 x 10²² kg, radius of moon = 1740 km.
- Answer 4:
- Question 5:
A boy weighing 60 kg f is wearing shoes with heel area of cross-section 20 cm² while a girl weighing 45 kg f wearing shoes with heel of area of cross-section 1.5 cm². Compare the pressure exerted on ground by their heels when they stand on the heel of one foot.
- Answer 5:
The girl’s shoe heel exerts a pressure 10 times more than the boy’s shoes heel
- Question 6:
A car weighs 1200 kg. This weight is evenly distributed on 4 wheels. If the pressure in each Tyre is 15 kg wf/cm², what is the area of each Tyre in contact.
- Answer 6:
- Question 7:
A block of wood is kept on a table top. The mass of the wooden block is 5 kg and its dimensions are 40 cm x 20 cm x 10 cm. Find the pressure exerted by the wooden block on the table top if it is made to lie on the table with its sides of dimensions (a) 20 cm x 10 cm (b) 40 cm x 20 cm. given g = 9.8 m/s².
- Answer 7:
(a) 2450 Pa (b) 612.5 Pa
- Question 8:
Relative density of silver is 10.8. The density of water is 10³ kg/m³. What is the density of silver in SI units?
- Answer 8:
10.8 x 10³ kg/m³
- Question 9:
The mass of an empty 40 litre petrol tank of a vehicle is 8.0 kg. What will be its mass when filled completely with fuel of density 700 kg/m³.
- Answer 9:
- Question 10:
An iron cylinder of radius 1.4 cm and length 8 cm is found to weigh 369.6 g. Calculate the density of iron.
- Answer 10:
- Question 11:
A solid of density 5000 kg/m^3 weigh 0.5 kg f in air. It is completely immersed in water of density 1000 kg/m³.
(a) Calculate the apparent weight of solid in water.
(b) What will be its apparent weight if water is replaced by liquid of density 8000 kg/m³?
- Answer 11:
(a)0.4 kg f (b) zero
- Question 12:
The mass of a block made of certain material is 13.5 kg and its volume is 15 x 10-³ m³. Will the block float or sink in water? Give reason for your answer.
- Answer 12:
The block floats.
- Question 13:
Why are sleeper used below the rails?
- Answer 13:
Sleeper are placed below the rails to increase area (A) and to consequently decrease pressure (P) due to weight (W) of a train on the rails as P= F/A = W/A (∙.∙ F = W). This prevents the railways line from sinking into ground.