Question

Q. Akshit is a student of class IX. He was waiting for a bus on a bus stand. He saw an old man trying to
keep his box on the roof of a bus but was unable to do so. Akshit picked up his box and placed the box on
the roof of the bus. The old man thanked Akshit.
Answer the following questions based on the above paragraph.
(1) Work done by Akshit while placing the box on the roof of the bus is
(a) Positive
(b) Negative
(c) Zero
(d) None of these
(ii) What is the work done by gravity on the box.
(a) Negative
(b) positive
(c) Zero
(d) None of these
(iii) What is the S. I. unit of work done?
(a) Newton
(b) Joule
(c) Joule sec
(d) All of these
iv) write the S.I. unit of gravity
a) m/s
b) m/s²
c) dyne
d) kg m/s²​

Answer 1

Answer:

1. positive

2. negative

3. joule

4. m/s2

Answer 2

1) Work done by Akshit while placing the box on the roof of the bus is (a) Positive

In this situation, Akshit applies force on the box in the upward direction and the displacement of the box is also in the upward direction. The force and the displacement have the same direction, Thus, the work done will be positive.

(ii) What is the work done by gravity on the box (a) Negative

In this situation, the gravitational force is acting in downwards direction and the displacement of the box is in upward direction. The angle between the displacement of the box and the force is 180°. Therefore, the work done will be negative.

(iii) What is the S. I. unit of work done (b) Joule.

Joule is the unit of energy and work is a form of energy. Therefore, the work done will also have the unit Joule.

iv) write the S.I. unit of gravity d) kg m/s².

The gravitational force on an object is given as

F = mg , where m is the mass of the object and g is the acceleration due to gravity.

The SI unit of mass is Kg and the SI unit of acceleration is m/s²

F = kg $\frac{m}{s^{2} }$

So, the SI unit of gravity is  kg $\frac{m}{s^{2} }$.