## Work done is defined as the dot product of:

A. Force and acceleration
B. Force and area
C. Force and instantaneous velocity
D. Force and displacement

Correct Answer: D. Force and displacement

Work done is defined as the dot product of Force vector and displacement vector. W = F.s Work done is a scalar quantity. Note: Instantaneous power is defined as the dot product of the Force vector and instantaneous velocity.

## The thrust on the rocket is:

A. in the same direction as the rocket
B. in the opposite direction of the rocket
C. at 90° to the direction of the rocket
D. None of the above

Correct Answer: B. in the opposite direction of the rocket

The thrust on the rocket is in the opposite direction of the rocket. The thrust is the force with which the rocket moves upwards. F = -u (dm/dt).

## What is the dot product of two perpendicular vectors?

A. 1
B. 0
C. -1
D. 1/2

When two vectors are perpendicular to each other, then θ = 90° and Cos 90° = 0 . Therefore, A.B = A x B x Cos θ = A x B x Cos 90° = 0.

## What is the apparent weight of the person when the elevator is accelerating downwards?

A. equal to the actual weight
B. greater than the actual weight
C. less than the actual weight
D. Zero

Correct Answer: C. less than the actual weight

The apparent weight of the person becomes less than the actual weight when the elevator is accelerating downwards. The apparent weight of the person becomes more than the actual weight when the elevator is accelerating upwards.

## What is the maximum height that can be attained by a projectile?

A. equal to its maximum range
B. one half of its maximum range
C. one-fourth of its maximum range
D. twice of its maximum range

Correct Answer: C. one-fourth of its maximum range

The maximum height that can be attained by a projectile is equal to one-fourth of its maximum range.

## Which Statment is correct about Kinetic energy during the projectile motion?

A. it is minimum at the point of projection
B. it is minimum at the highest point
C. it is maximum at the highest point
D. it is minimum at the point of reaching the ground

Correct Answer: B. it is minimum at the highest point

The Kinetic energy of an object is maximum at the point of projection or at the point of reaching the ground. It is minimum at the highest point.

## The magnitude of the resultant of two vectors is maximum in which of the following case?

A. when vectors act in the same direction
B. when vectors act in the opposite direction
C. when vectors act at 90° to each other
D. None of the above

Correct Answer: A. when vectors act in the same direction

The magnitude of the resultant of two vectors is maximum when vectors act in the same direction. The magnitude of the resultant of two vectors is minimum when vectors act in opposite directions.

## Joule/kg is the S.I unit of which of these physical quantities?

A. Entropy
B. Permittivity of free space
C. Latent heat
D. Gas constant

Joule/kg is the S.I unit of Latent heat (L) = heat(Q)/mass(m) Latent heat is the heat required to convert a solid into a liquid or vapor, or a liquid into a vapor, without any change in temperature.

## 1 femto metre is equal to how many metres?

A. 10-12
B. 10-14
C. 10-15
D. 1-24

1 femto metre is equal to 10-15 metre. Some other metric prefixes are:

• nano = 10-9
• pico = 10-12
• atto = 10-18
• tera = 1012
• peta = 10-15
• exa = 10-18

A. Celsius
B. Fahrenheit
C. Kelvin
D. Rankine