Motion
In Text Question Answer
Part 2
Question 8: During an experiment, a signal from a spaceship reached the ground station in five minutes. What was the distance of the spaceship from the ground station? The signal travels at the speed of light, that is, 3 × 108 ms-1.
Answer: Here, we have, speed `=3xx10^8\ ms^(-1)`
Time = 5 minute
`=5xx60s=300` second
We know that, Distance = Speed x Time
⇒ Distance `=300xx3xx10^8\ ms^(-1)`
`= 900 xx 10^8\ m`
`=9xx10^10m`
Question 9: When will you say a body is in
(i) uniform acceleration?
Answer: When rate of change of motion is same in equal intervals of time.
(ii) non-uniform acceleration?
Answer: When rate of change of motion is not same in equal intervals of time.
Question 10: A bus decreases its speed from 80 km/h to 60 km/h in 5 s. Find the acceleration of the bus.
Answer: Here we have, u=80 km/h `=80xx5/(18)=(200)/9` m/s
v=60 km/h `=60xx5/(18)=(50)/3` m/s and `t=5s`
∴ Acceleration (a) =?
We know that `v=u+at`
Or, `a=(v-u)/t`
`=((50)/3-(200)/9)/5=-(50)/(9xx5)`
`=-(10)/9` m s-2
Question 11: A train starting from a railway station and moving with uniform acceleration attains a speed of 40 km/h in 10 minutes. Find its acceleration.
Answer: Here we have,
Initial velocity, u = 0,
Final velocity, v = 40km/h `=40xx5/(18)=(100)/9` m/s
Time (t) = 10 minute = 60 × 10 = 600s
Acceleration (a) =?
We know that `v=u+at`
Or, `a=(v-u)/t`
`=(100)/(9xx600)=1/(54)` m s-2
Question 12: What is the nature of the distance-time graphs for uniform and non-uniform motion of an object?
Answer:
(a) The slope of the distance-time graph for an object in uniform motion is straight line.
(b) The slope of the distance-time graph for an object in non-uniform motion is not a straight line.
Question 13: What can you say about the motion of an object whose distance-time graph is a straight line parallel to the time axis?
Answer: When the slope of distance-time graph is a straight line parallel to time axis, the object is moving with uniform motion.
Question 14: What can you say about the motion of an object if its speed-time graph is a straight line parallel to the time axis?
Answer: When the slope of a speed time graph is a straight line parallel to the time axis, the object is moving with uniform speed.