Science M.C.Q. [1 M]

4. There must be a relative motion between the coil of wire and a magnet.

4. All the above.

Explanation:

Retardation is opposite of acceleration.

In case of acceleration, velocity increases with time and in case of retardation, velocity decreases over time.

1. Zero

Explanation:

Acceleration of a body is defined as the rate of change of the velocity of the body.

Now since the velocity doesn't change at all, the rate of change will be zero.

So, acceleration = 0

1. Direction of motion changes

Explanation:

Uniform circular motion is accelerated because the velocity changes due to continuous change in the direction of motion.

Thus, for a body moving in a circular path at a constant speed, its velocity changes continuously.

The change in velocity gives rise to an acceleration in the moving body.

3. In merry-go-round.
   Explanation:
   The speed is constant but velocity is not constant, because its direction goes on changing i.e., there is acceleration in the motion. So, we can say that the boy is in accelerated motion.

4. 0km

4. A radial acceleration

Explanation:

Velocity is not constant since the direction of the ball changes every instance.

The ball has radial acceleration since there is a centripetal force acting on it towards the center.

Ball moving in a circular path has tangential velocity.Cutting the thread, the ball moves tangentially

3. The actual path travelled by the body between the initial and final positions

Explanation:

Distance is defined as the length of the actual path travelled by a moving body between its initial and final positions.

1. The stone flies off tangential to the circle of rotation

Explanation:

When a stone is going around a circular path, the instantaneous velocity of stone is acting as tangent to the circle.

When the string breaks, the centripetal force stops to act.

Due to inertia, the stone continues to move along the tangent to circular path.

So, the stone flies off tangentially to the circular path

2. The velocity of an object may be zero but acceleration is not zero.

3. 37.5m

2. Uniform speed

Explanation:

If the speed-time graph is parallel to the time axis, then this means that the body has the same speed at all the time.

Thus, speed = constant

1. 0

Explanation:

When the direction is changed then velocity changes but the speed or magnitude of velocity remains constant.

In this case, the truck changes only the direction of motion, not the magnitude.

So change in the magnitude of velocity is zero.

4. Both acceleration and speed are constant

Explanation:

For a body moving in uniform circular motion the speed attained  by the object will remain constant not the velocity as velocity depends on the direction of motion, and in circular motion the direction of the object changes at every point.

As speed remains constant the acceleration will remain constant.

3. constant velocity and a varying speed

Explanation:

Speed of body is magnitude of velocity. So if velocity is only changing direction then speed is constant.

But if speed is changing then velocity have to be varying.

When a body starts moving the incident when t=0 then it have zero velocity but some acceleration is there.

Object moving with constant velocity has zero acceleration but non zero speed.

1.  Zero velocity

Explanation:

According to the given condition in the question, The Distance-time graph is horizontal and straight line as given in the above image.here the position of object is not changing with respect to time. 

3. Changes direction

Explanation:

When a particle is under uniform circular motion, its direction of motion continuously changes, hence the magnitude of its velocity remains constant while its direction changes.

1. Velocity determines direction of motion of a body

Explanation:

Velocity, being a vector, gives the direction of the change of position of a body.

Hence it determines the direction of motion of a body.

In contrast, acceleration doesn't need to relate to the direction of motion.

3. Acceleration.

Explanation:

The rate of change of speed per unit time is termed as acceleration.

1. 200m

1. 8m/s, 2m/s

Explanation:

Let the objects speed be x and y respectively, when moving towards each other:

x + y = 10 ...(1)

and, when moving in same direction

x - y = 6 ...(2)

now,

adding 1 and 2 we get

2x = 16m/s

x = 8m/s

and,

putting this in 1

y = 2m/s

The speed of the bodies is 8m/s² and 2m/s².

1. Direction of motion changes

Explanation:

An accelerating body is an object that is changing its velocity.

And since velocity is a vector that has both magnitude and direction, a change in either the magnitude or the direction constitutes a change in the velocity.

4. Angular speed

Explanation:

As an object moves around in a circle at constant speed (uniform circular motion), both the velocity and the acceleration change.

The magnitudes of the velocity and acceleration don't change, but since velocity and acceleration are vectors, the fact that their directions change means that they change.

Momentum is directly proportional to the velocity of the body and hence it changes.

In the uniform circular motion, the angular speed is same for all the particles,

2. Electrical energy into mechanical energy.

4. 4

1. Yes, Uniform Circular Motion.

Explanation:

Yes it is possible. Let us take an example, circular motion.

In this it has acceleration because direction of motion is changing but it has constant speed  along tangential.

Hence it is possible.

3. 2r
   Explanation:
   Displacement is the minimum distance between the initial position and final position.
   After moving half circle (A to B) displacement will be AB
   AB is diameter i.e. 2r

1. Change in position in a certain direction

Explanation:

Displacement is the linear distance between the initial and final positions.

So, it is change in position in a certain direction.

2. Velocity

Explanation:

Velocity is the rate of change of displacement

3. All parts of the ball have the same velocity (magnitude and direction) and the velocity is constant.

Explanation:

In uniform translatory motion, all parts of the ball have the same velocity in magnitude and direction and this velocity is constant.

4. Maxwell

2. Speed

Explanation:

In a uniform circular motion, the direction of velocity changes but its magnitude remains constant, hence, speed remains constant in a uniform circular motion.

3. ms²

3. A van slowing down as it approaches a stop sign

Explanation:

A object is said to have an acceleration if it changes its velocity either by increasing its speed, decreasing its speed or changing the direction of its velocity.

Since the car and the truck move with constant speed, thus they have zero acceleration.

But the van is slowing down its speed, thus it has deacceleration.

2. Displacement
   Explanation:
   Displacement is the shortest distance joining initial and final points through a straight line

1. 6m/s

4. Equal to 1 or less than 1

Explanation:

Displacement is always smaller than or equal to displacement.

1. Uniform acceleration.

3. In accelerated motion.
   Explanation:
   In merry-go-round, the speed is constant but velocity is not constant, because its direction goes on changing i.e., there is acceleration in the motion.
   So, we can say that the boy is in accelerated motion.

3. 392ms⁻¹

2. Displacement.

3. Its acceleration is zero.

1. Motion in straight line.

1. That the body is moving away from the reference point

2. Uniform acceleration.

Explanation:

The displacement of the body in equal interval of time is unequal, but acceleration is constant. The acceleration will thus be uniform.

1. Acceleration increases velocity, retardation decreases it