Question

(a) “The acceleration of an object could be zero even when several forcesis acting on
it”. Do you agree with the statement? Why? Givereasons
(b) Mention the relation between kilowatt-hour (KWh) and Joule(J).
(c) Calculate the power of an engine required to lift 10ʻKg of coal per hour from a mine
of 360 meterdeep​

Answer 1

a) Yes.

The acceleration of an object could be zero even when several forces are acting on it.

It can happen when the forces acting on a body cancels out each other and the resultant force is zero.

b) Relation between kilowatt hour and joule -

1 kWh = 3.6 × 10⁶ J

c)

Given :-

• m = 10 kg
• g = 9.8 m/s²
• h = 360 m
• t = 1 hour = 3600 sec

To find :-

• Power

Solution :-

We know that,

Power = m × g × h / t

Substituting the values :-

⇒ P = 10 × 9.8 × 360 / 3600

⇒ P = 35280 / 3600

⇒ P = 9.8

Power of engine required = 9.8 J