**Explanation:**

The velocity of car A relative to car B is (10km/h+40km/h)=50km/h

**Answer:**

Option (B) is correct.

**Explanation:**

Given that the molecules of hydrogen gas () react with molecules of oxygen gas () in a sealed reaction chamber to produce water ().

The governing equation for the reaction is

From the given, the **only fact that can be observed** that 2 moles of and 1 mole of reacts to produce 2 moles of .

As the mass of 1 mole of grams ... (i)

The mass of 1 mole of grams ...(ii)

The mass of 1 mole of grams (iii)

Now, the **mass of the reactant** = Mass of 2 moles of + mass 1 mole of

[ using equations (i) and (ii)]

grams.

**Mass of the product **= Mass of 2 moles of

[ using equations (iii)]

=36 grams

As the mass of reactants = mass of the product.

So, mass is conserved.

Hence, option (B) is correct.

**Answer:**

0.00321 Nm

**Explanation:**

= Final angular velocity = 3.5 rad/s

= Initial angular velocity = 0

= Angular acceleration

= Angle of rotation = 2 rev

Equation of rotational motion

Moment of inertia is given by

Torque is given by

**The torque required is 0.00321 Nm**