1Exercises12 questions
Q.1Classify the following as motion along a straight line, circular or oscillatory motion:
(i) Motion of your hands while running.
(ii) Motion of a horse pulling a cart on a straight road.
(iii) Motion of a child in a merry-go-round.
(iv) Motion of a child on a see-saw.
(v) Motion of the hammer of an electric bell.
(vi) Motion of a train on a straight bridge.v
Answer:(i) Oscillatory motion
(ii) Motion along a straight line
(iii) Circular motion
(iv) Oscillatory motion
(v) Oscillatory motion
(vi) Motion along a straight line
Q.2Which of the following are not correct?
(i) The basic unit of time is second.
(ii) Every object moves with a constant speed.
(iii) Distances between two cities are measured in kilometres.
(iv) The time period of a given pendulum is not constant.
(v) The speed of a train is expressed in m/h.v
SolutionObjects can move with variable speed. The time period of a given pendulum remains nearly constant for small oscillations. Speed of a train is usually expressed in km/h, while the SI unit of speed is m/s.
Answer:Statements (ii), (iv) and (v) are not correct.
Q.3A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?v
SolutionTime period = total time taken / number of oscillations = 32 s / 20 = 1.6 s.
Answer:The time period is 1.6 s.
Q.4The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.v
SolutionSpeed = distance / time = 240 km / 4 h = 60 km/h.
Answer:The speed of the train is 60 km/h.
Q.5The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the car, if at 08:50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/h also.v
SolutionDistance = 57336.0 - 57321.0 = 15.0 km. Time = 20 min. Speed = 15.0 / 20 = 0.75 km/min. In km/h, 0.75 × 60 = 45 km/h.
Answer:The car travels 15.0 km. Its speed is 0.75 km/min, or 45 km/h.
Q.6Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/s, calculate the distance between her house and the school.v
SolutionTime = 15 min = 15 × 60 = 900 s. Distance = speed × time = 2 m/s × 900 s = 1800 m = 1.8 km.
Answer:The distance between Salma's house and school is 1800 m, or 1.8 km.
Q.7Show the shape of the distance-time graph for the motion in the following cases:
(i) A car moving with a constant speed.
(ii) A car parked on a side road.v
SolutionIn a distance-time graph, constant speed gives a straight sloping line, while zero speed gives a horizontal line.
Answer:(i) For a car moving with constant speed, the distance-time graph is a straight sloping line.
(ii) For a parked car, the graph is a horizontal straight line because distance from the starting point does not change with time.
Q.8Which of the following relations is correct?
(i) Speed = Distance × Time
(ii) Speed = Distance/Time
(iii) Speed = Time/Distance
(iv) Speed = 1/Distance × Timev
- a. speed = distance × time
- b. speed = distance / time
- c. speed = time / distance
- d. speed = 1 / distance × time
SolutionSpeed is the distance travelled in unit time.
Answer:(ii) Speed = Distance/Time
Q.9The basic unit of speed is:
(i) km/min (ii) m/min (iii) km/h (iv) m/sv
- a. km/min
- b. m/min
- c. km/h
- d. m/s
SolutionThe SI unit of distance is metre and the SI unit of time is second, so the SI unit of speed is m/s.
Q.10A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is:
(i) 100 km (ii) 25 km (iii) 15 km (iv) 10 kmv
Solution15 min = 0.25 h. First distance = 40 × 0.25 = 10 km. Second distance = 60 × 0.25 = 15 km. Total distance = 10 + 15 = 25 km.
Q.12Fig. 9.15 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster? In the graph, both lines start from the origin; line A is steeper than line B.v
SolutionFor distance-time graphs, the steeper line represents greater speed.
Answer:Vehicle A is moving faster because its distance-time graph is steeper than that of vehicle B.
Q.13Which of the following distance-time graphs shows a truck moving with speed which is not constant? The options are: (i) a straight sloping line; (ii) a horizontal line; (iii) a curved line rising more steeply with time; (iv) a straight sloping line through the origin.v
SolutionA straight distance-time graph means constant speed; a curved graph means changing speed.
Answer:(iii). A curved distance-time graph shows that the speed is changing, so the speed is not constant.