Question of Exercise 1

Question A distance is always :

Option 1 shortest length between two points

Option 2 path covered by an object between two points

Option 3 product of length and time

Option 4 none of the above

A man throws the ball with the same speed vertically upwards one

after the other at an interval of 2 seconds. What should be the speed of the throw so that more than two balls are in the sky at any time? (Given g = 9.8 m/s^2)

A: More than 19.6 m/s

B: At least 9.8 m/s

C: Any speed less than 19.6 m/s

D: Only with speed 19.6 m/s

Solution:

Explanation

Given:t =2s ;g =9.8 m/s2

When the ball is thrown upward the final velocity become zero.i.e v =0

Now, Time taken by ball to reach maximum height

v =u - gt

O =u - gt

u = gt

On substituting the given, we get

u =9.8×2

u = 19.6 m/s

As a result, when he throws a ball at a minimum speed of in19.6 m/s a 2s time period, two balls can be in the air at the same moment.

The correct answer is A i.e More than 19.6 m/s.

The strength of force is expressed by

A: Direction

B: Magnitude

C: Both

D: None

Solution:

Explanation:

The strength of the force can be expressed by the magnitude because force can be smaller and larger in magnitude.

Correct option is (B)

The strength of the force can be expressed by the magnitude.

The relation between frequency f and time period T is given by

A: f = T

B: f =  1/T

C: T=f2

D: T=f3

Solution:

Explanation:

Frequency can be defined as a number of complete oscillation in one second

And the time period is the time which is required to complete one complete oscillation.

The frequency and the time period is reciprocal to each other.Hence option(B) is correct.

What is time period Write its S.I unit

Solution:

Explanation:

The time Period can be defined as the time taken to complete one oscillation in the dense medium.

The S.I unit of time period is second.

The time taken by a particle of medium to complete its one vibration is called the time period of the wave.

The S.I unit will be second.

A sonar device on a submarine sends out a signal and receives an echo 5 s later

Calculate the speed of sound in water if the distance of the object from the submarine is 3625 m.

Solution:

Ans. Given,

Time taken = 5 seconds

The time taken by ultrasound signal to travel from the submarine to the object will be half of this time:

=5/2

= 2.5 seconds

We know that,

Speed = Distance/Time

= 3625/2.5m

= 1450 m/s

Therefore, the speed of sound is 1450 m/s.