Page No: 19
Q1. Is displacement a scalar quantity?
Answer:
Displacement is not a scalar quantity, it is a vector quantity.
Q2. State whether the distance is a scalar or a vector quantity.
Answer:
Distance is a scalar quantity.
Q3. Change the speed of 6 m/s to km/h.
Answer:
6 m/s = 6×(3600/1000) km/h = 21.6 km/h.
Q4. What name is given to the speed in a specified direction?
Answer:
Velocity is the name that is given to the speed in a specified direction.
Q5. Give two examples of bodies having non-uniform motion.
Answer:
a) Bus moving on the road
b) A racing horse motion
Q6. Name the physical quantity obtained by diving ‘distance travelled’ by ‘time taken’ to travel that distance.
Answer:
Speed is the physical quantity that is obtained from distance travelled and time taken. Speed is defined as the distance travelled per unit time.
Q7. What do the following measure in a car?
a) speedometer
b) odometer
Answer:
a) Speedometer in a car is used for measuring the instantaneous speed of the car.
b) Odometer in a car is used for recording the distance travelled by the car.
Q8. Name the physical quantity which gives us an idea of how slow or fast a body is moving.
Answer:
To know how slow or fast the body is moving, speed is used.
Q9. Under what conditions can a body travel a certain distance, and yet its resultant displacement be zero?
Answer:
The resultant displacement of a body is said to be zero when the body comes back to its starting point and covers a certain non-zero distance.
Q10. In addition to speed, what else should we know to predict the position of a moving body?
Answer:
Along with speed, the direction of the body should be known.
Q11. When is a body said to have uniform velocity?
Answer:
A body is said to have a uniform velocity when it covers equal distances in equal intervals of time in a particular distance.
Q12. Under which condition is the magnitude of average velocity equal to average speed?
Answer:
The magnitude of average velocity is equal to the average speed when the object moves in a single straight line.
Q13. Which of the two can be zero under certain conditions: average speed of a moving body or average velocity of a moving body?
Answer:
The average velocity of a moving body can be zero.
Q14. Give one example of a situation in which a body has a certain average speed, but its average velocity is zero.
Answer:
When a car moves from the parking area to the mall and back from the mall to the parking area, the average speed is certain, but the average velocity is zero.
Q15. What is the acceleration of a body moving with uniform velocity?
Answer:
The acceleration of a body is zero that has a uniform velocity.
Q16. What is the other name for negative acceleration?
Answer:
Negative acceleration is also known as retardation.
Q18. What type of motion is exhibited by a freely falling body?
Answer:
Uniformly accelerated motion
Q19. What is the SI unit of retardation?
Answer:
SI unit of retardation is m/s2.
Q20. Fill in the following blanks with suitable words:
a) Displacement is a ……… quantity whereas distance is a ……….
b) The physical quantity which gives both the speed and direction of motion of a body is called its ……….
c) A motorcycle has a steady ………. of 3 m/s2. This means that every ……….. its …………. increases by ………….
d) Velocity is the rate of change of ……….. it is measured in ……….
e) Acceleration is the rate of change of ………. it is measured in …….
Answer:
a) Vector and scalar
b) Velocity
c) Acceleration, second, velocity, 3m/s
d) Displacement, m/s
e) Velocity, m/s2
Short Answer Type Questions
Q21. What type of motion, uniform or non-uniform, is exhibited by a freely falling body? Give reason for your answer.
Answer:
A freely falling body has a non-uniform motion because in the initial 1 second, the distance covered is small, and in the later 1 second, the distance covered is large. As the distance covered is uneven, the motion is non-uniform.
Q22. State whether the speed is a scalar or a vector quantity. Give reason for your choice.
Answer:
Speed is a scalar quantity as it has only magnitude, and there is no specific direction.
Q23. Bus X travels a distance of 360km in 5 hours, whereas bus Y travels a distance of 476lm in 7 hours. Which bus is faster?
Answer:
For bus X,
Speed = distance/time
Speed = 360/5 = 72 km/h
For bus Y,
Speed = 476/7 = 68 km/h
Therefore, the speed of bus X is more than the bus Y.
Q24. Arrange the following speeds in increasing order:
a) an athlete running with a speed of 10 m/s
b) a bicycle moving with a speed of 200 m/min
c) a scooter moving with a speed of 30 km/h
Answer:
Speed of athlete = 10 m/s
Speed of bicycle = 200 m/min = 200/60 m/s = 3.33 m/s
Speed of scooter = 30 km/h = 30000/3600 m/s = 8.33 m/s
Therefore, bicycle < scooter < athlete
Q25. a) Write the formula for acceleration. Give the meaning of each symbol which occurs in it.
b) A train starting from the railway station attains a speed of 21 m/s in one minute. Find its acceleration.
Answer:
a) Acceleration = final velocity – initial velocity/ time taken
b) u = 0 m/s
v = 21 m/s
t = 1 min = 60s
a = v-u/t = 0.35 m/s2
