Revision 3 – Section B Questions with Answers
Question 6
1. A metallic spherical ball weighs 500 g. The volume of this ball is 30 cm³. Calculate its density.
Density = Mass ÷ Volume = 500 g ÷ 30 cm³ = 16.67 g/cm³
2. Convert 27 m/s to km/h.
1 m/s = 3.6 km/h
27 × 3.6 = 97.2 km/h
27 × 3.6 = 97.2 km/h
3. Mahesh weighs a piece of iron of mass 40 kg at the poles and the equator. Will there be a difference in its weight? Why?
Yes, weight is slightly less at the equator than at the poles due to lower value of acceleration due to gravity (g) at the equator caused by Earth's rotation.
4. Consider an object of mass m moving with kinetic energy K. If the velocity is halved, how much mass should be reduced for KE to remain same?
KE = ½ m v². If v → v/2, KE = ½ m (v²/4) = (¼)(½ m v²).
To keep KE same, mass must be increased 4 times.
So, reduce mass to ¼th if velocity doubles, but for halving velocity → mass must be 4m.
To keep KE same, mass must be increased 4 times.
So, reduce mass to ¼th if velocity doubles, but for halving velocity → mass must be 4m.
5. Differentiate between uniform and non-uniform motion.
Uniform Motion: Object covers equal distances in equal intervals of time.
Non-uniform Motion: Object covers unequal distances in equal intervals of time.
Non-uniform Motion: Object covers unequal distances in equal intervals of time.
6. Give a practical example showing conversion of potential energy into kinetic energy.
A swinging pendulum: At extreme position, it has maximum potential energy. As it moves, potential energy converts into kinetic energy at mean position.
Question 7
1. Define a graduated cylinder. Explain the displacement method.
Graduated Cylinder: A cylindrical container marked with volume readings used to measure liquid volume.
Displacement Method: Note initial water level, immerse solid, note final water level. The difference gives the volume of irregular solid.
Displacement Method: Note initial water level, immerse solid, note final water level. The difference gives the volume of irregular solid.
2. What is the time period of a simple pendulum? Effect of change in mass or material of the bob?
Time period (T) = Time taken for one complete oscillation.
T depends only on length and g, not on mass or material of bob. So, no effect.
T depends only on length and g, not on mass or material of bob. So, no effect.
3. Ramesh moves on a circular path (r=21 m) and Ram on a square path (side=20 m). Find distance covered. Same displacement?
Distance by Ramesh = 2Ï€r = 2 × 3.14 × 21 = 132 m.
Distance by Ram = 4 × 20 = 80 m.
Displacement after one round = 0 for both, since they return to start point.
Distance by Ram = 4 × 20 = 80 m.
Displacement after one round = 0 for both, since they return to start point.
4. Define average speed.
Average speed = Total distance travelled ÷ Total time taken.
Question 8
1. Calculate the volume of a room 6 m × 8 m × 10 m.
Volume = Length × Breadth × Height = 6 × 8 × 10 = 480 m³
2. Moksh has mass 50 kg. Can his weight be zero in any situation?
Yes,i) at the centre of the earth. ii)during free fall or in space (weightlessness) where gravitational pull is not effective, his apparent weight is zero.
3. What is muscular energy? From where is it obtained?
Muscular energy is energy produced by muscles to perform work. It is obtained from chemical energy of food.
4. What are the energy changes while producing hydroelectricity? Define these forms of energy.
Water at height: Potential Energy → Moving water: Kinetic Energy → Turbine: Mechanical Energy → Generator: Electrical Energy.
These forms: Potential (stored due to position), Kinetic (motion), Electrical (usable current).
These forms: Potential (stored due to position), Kinetic (motion), Electrical (usable current).
