How do i solve 16th qns.? answer asap

It really doesn't matter whether the two masses are joined by a light string, a light reinforced concrete and steel frame, a light coating of strong glue, or a layer of scotch tape that's one atom thick.  They look like a single mass of 10 kg.

Part a). Force = (mass) x (acceleration)

The acceleration of 10 kg of mass pulled with 100N of force is

100 N = (10 kg) x (acceleration)

Divide each side by (10 kg):  

Acceleration = (100 N) / (10 kg)

Acceleration = 10 m/s²

Part b).  Now look at just the rear 16 kg.  It stays hooked onto the front 4 kg, and everything moves together.  So both pieces must have the same distance, velocity, acceleration etc.  We know that the acceleration is 10 m/s² .

Force = (mass) x (acceleration)

Force on the rear 16 kg = (16 kg) x (10 m/s²)

Force = 160 Newtons

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