## Class 9 - Physics

**Question:**

**Answer:**

[Ans. 36 kg]

## Questions and Answers

**Motion**- Questions

Which of the following situation is impossible to have?

Scene I: Object moving to east with velocity (v) and acceleration is acting towards west.

Scene II: Object is moving with variable velocity but fixed acceleration.

Scene III: Object is moving with uniform velocity but non-uniform acceleration.

Scene IV: Object is moving with uniform speed but variable acceleration.

(a) It cannot be zero.

(b) Its magnitude is greater than the distance travelled by the object.

Fill in the blanks :

If the position of an object does not change with time, it is said to be at _____.

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 × 10^{8} m s^{–1}.

Consider the following two scenarios and tell in which case average speed is harmonic mean or arithmetic mean?

Case 1: A fellow travels from city A to city B. For the first hour, he drove at the constant speed of 20 km/hr. Then he (instantaneously) increased his speed and, for the next hour, kept it at 30 km per hour. Find the average speed of the motion.

Case 2: A fellow travels from city A to city B. The first half of the way, he drove at the constant speed of 20 km per hour. Then he (instantaneously) increased his speed and traveled the remaining distance at 30 km per hour. Find the average speed of the motion.

A particle moves along the x axis from A to B. Which Of the following values of the initial and final coordinates, which results in a negative displacement?

(a) A = 4m, B = 6m

(b) A = −4m, B = −2m

(c) A = −4m, B = −8m

(d) A = −4m, B = 2m

What is the nature of the distance-time graphs for uniform and non-uniform motion of an

object?

(a) magnitude only

(b) direction only

(c) both direction and magnitude

(d) none of these

A driver of a car travelling at 52 km/h applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5 s. Another driver going at 3 km/h 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?

A racing car has a uniform acceleration of 4 m s^{–2}.

What distance will it cover in 10 s after start?

The equation v = u + at gives information as

(a) velocity is a function of time.

(b) velocity is a function of position.

(c) Position is a function of time.

(d) Position is function of velocity and time.

Fill in the blanks :

The rate of change of velocity of a moving body with time is called ______.

A car travels along a straight line and covers one third of total distance with speed of 4 m/s. The remaining distance, it covers with a speed of 2 m/s half the time and with speed of 6m/s for the other half time. Find the average speed of the car.

An object has moved through a distance. Can it have zero displacement? If yes, support your answer with an example.

Fig (below) shows the distance-time graph of three objects A,B and C. Study the graph and answer the following questions:

(a) Which of the three is travelling the fastest?

(b) Are all three ever at the same point on the road?

(c) How far has C travelled when B passes A?

(d) How far has B travelled by the time it passes C?

A farmer moves along the boundary of a square field of side 10 m in 40 s. What will be the magnitude of displacement of the farmer at the end of 2 minutes 20 seconds?

The equation S = ut + ½at^{2} gives information as

(a) velocity is a function of time.

(b) velocity is a function of position.

(c) Position is a function of time.

(d) Position is function of velocity and time.

A train is travelling at a speed of 90 kmh^{–1}. Brakes are applied so as to produce a uniform acceleration of – 0.5 ms^{–2}. Find how far the train will go before it is brought to rest.

The speed-time graph for a car is shown is figure below.

(a) Find how far does the car travel in the first 4 seconds. Shade the area on the graph that represents the distance travelled by the car during the period.

(b) Which part of the graph represents uniform motion of the car?

^{–2}. What will be its velocity 3 s after the start?

A bus starting from rest moves with a uniform acceleration of 0.1 ms^{–2} for 2 minutes.

Find (a) the speed acquired, (b) the distance travelled.

(a) Calculate the apparent weight of the solid in water.

(b) What will be its apparent weight if water is replaced by a liquid of density 8000 $Kg/m3$ ?

(i) distance travelled from O to A.

(ii) distance travelled from B to C.

(iii) total distance travelled by the body in 16 sec.