Advertisements
Advertisements
Question
A spaceship is moving in space with a velocity of 60 kms−1. It fires its retro engines for 20 seconds and velocity is reduced to 55 kms−1. Calculate the distance travelled by a spaceship in 40 s, from the time of firing of the retro- rockets.
Advertisements
Solution
Initial velocity of spaceship = u = 60 kms−1
Final velocity of spaceship = v = 55 kms−1
It decelerates for 20 s
t = 20 s
v = u + at
55 = 60 + a (20)
20a = 55 – 60
20a = −5
a = `(-5)/20`
a = − 0.25
distance travelled in the first 20 sec. = s = u × t − `1/2` a × t2
s = 60 × 20 − `1/2` × 0.25 × 202
= 1200 − `1/2` × 0.25 × 400
= 1200 − `1/2` × 100
= 1200 − 50
= 1,150 km.
After 20 sec. the velocity of the spaceship is constant at 55 km/sec. Hence, the distance travelled is = 55 × 20 = 1,100 km
The total distance travelled in 40 sec. = 1,150 + 1,100 = 2,250 km
APPEARS IN
RELATED QUESTIONS
What can you say about the motion of an object if its speed-time graph is a straight line parallel to the time axis?
A driver of a car travelling at 52 km h−1 applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5 s. Another driver going at 3 km h−1 in another car applies his brakes slowly and stops in 10 s. On the same graph paper, plot the speed versus time graphs for the two cars. Which of the two cars travelled farther after the brakes were applied?
Show the shape of the distance-time graph for the motion in the following case:
A car moving with a constant speed.
What can you say about the motion of a body whose distance-time graph is a straight line parallel to the time axis ?
Fill in the following blank with suitable word :
The slope of a speed-time graph of a moving body gives its………………………..
Show the shape of the distance – time graph for the motion in the following cases.
- A bus moving with a constant speed.
- A car parked on a road side.
Complete the data of the table given below with the help of the distance-time graph given in the figure.
| Distance (m) | 0 | 4 | ? | 12 | ? | 20 |
| Time (s) | 0 | 2 | 4 | ? | 8 | 10 |
Starting from A, Paheli moves along a rectangular path ABCD as shown in figure. She takes 2 minutes to travel each side. Plot a distance-time graph and explain whether the motion is uniform or non-uniform.
Distance between Bholu’s and Golu’s house is 9 km. Bholu has to attend Golu’s birthday party at 7 o’clock. He started from his home at 6 o’clock on his bicycle and covered a distance of 6 km in 40 minutes. At that point, he met Chintu and he spoke to him for 5 minutes and reached Golu’s birthday party at 7 o’clock. With what speed did he cover the second part of the journey? Calculate his average speed for the entire journey.
What do you infer if
- Distance – time graph is a straight line.
- The velocity-time graph is curved.
- Displacement time is zigzag.
