## Intermediate level

## Question no. 1

Choose which of the following comments is correct. The comments concern average and instantaneous velocities.

When a particle moves with constant velocity then its average velocity is equal to its instantaneous velocity, otherwise on the whole it is impossible.Average velocity is always not equal to instantaneous velocity since they are given by different formulae.

Average velocity is always equal to instantaneous velocity regardless of the motion a particle moves.

Instantaneous velocity is always greater than average velocity since the average velocity approaches the instantaneous velocity when Δt approaches zero.

## Question no. 2

A particle moves along the x direction and its position at time t is given by the following equation x(t)= x_{0} + v_{0}t - at^{2}/2. What would you say about the motion?

The particle moves with constant and positive acceleration.

The particle moves with constant and negative acceleration.

The particle moves with an acceleration but it is not constant.

## Question no. 3

In uniform circular motion the centripetal acceleration is given by a formula. Which one?

a_{d}= v

^{2}r,

a

_{d}= v

^{2}/ r ,

a

_{d}= r/ v

^{2},

a

_{d}= 1/ v

^{2}r .

## Question no. 4

Newton's First Law states that in the absence of forces, a particle:

remains stationary,continues to move with unchanging speed in the same direction,

continues to move with constant acceleration in the same direction ,

remains stationary or continues to move with unchanging speed in the same direction?

## Question no. 5

The work done by a force on a body is zero. What could have been the reason of that?

The force is zero or the displacement of the body is zero or the force is always perpendicular to the direction of motion of the body.The force is zero or the displacement of the body is zero or the force is always parallel to the direction of motion of the body.

The force is zero and the displacement of the body is zero and the force is always perpendicular to the direction of motion of the body.

The force is zero and the displacement of the body is zero and the force is always parallel to the direction of motion of the body.

## Question no. 6

Newton's Second Law can be stated in two ways:

1) **F** = m **a** or

2) lim_{Δt -> 0} Δ**p** / Δt = **F** ( or equally d**p** / dt = **F** ) .

Which form of the second law is more general and why?

The first form, since sir Isaac Newton it stated.

The second form, since it can be applied to the motion of a particle whose mass changes.

The two forms are completely equivalent.

The first form, since the force is always proportional to the acceleration.