1) lighting a match stick

2) permanent

3) physical

**Answer:**

Velocity includes direction.

**Explanation:**

Velocity is a vector. It includes both direction and magnitude.

Speed is the magnitude of velocity.

**Answer:**

Part a)

Part b)

Part c)

**Explanation:**

Part a)

As we know that the friction force on two boxes is given as

Now we know by Newton's II law

so we have

Part b)

For block B we know that net force on it will push it forward with same acceleration so we have

Part c)

If Alex push from other side then also the acceleration will be same

So for box B we can say that Net force is given as