Question

class 9 physics ch 2 numericals force and laws of motion​

Answer 1

Question 1 - An automobile vehicle has a mass of 1000 kg. What must be the force between the vehicle and road if the vehicle is to be stopped with a negative acceleration of 1.0 m/sec²?

Given :

Mass (m) = 1000 Kg

Acceleration (a) = -1.0 m/sec²

To Find :

Force

Solution :

As per the second law of motion,

F = ma

F = 1000kg × (-1.0 ms-2) = -1000 N

Hence, the force between the automobile and the road acting opposite to the automobile's motion is -1000 N.

Question 2 - A stone of 1 kg is thrown with a velocity of 10 ms-1 across the frozen surface of a lake and comes to rest after travelling a distance of 10 m. What is the force of friction between the stone and the ice?

Given :

Mass of the stone (m) = 1 Kg

Initial velocity (u) = 10 m/sec

Final velocity (v) = 0

Distance travelled (s) = 10 m

To Find :

Force of friction between the stone and the ice.

Solution :

We know,

      v² = u² + 2as

Substituting the values in the above equation we get,

⇒       0² = (10)² + 2(a)(10)

⇒   -100 = 20a

∴          a =  - 5 m/s² (retardation)

As Force (F) =  Mass (m) × Acceleration (a)

We get,

F = 1 × (-5) = -5N

Here the negative sign indicates the opposing force which is Friction.

Hence, the frictional force is 5 N.