National Science Olympiad Model Paper 3 Questions and Answers Part 24

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5. Three blocks A, B and C of masses 6 kg, 4 kg and 2 kg respectively, are in contact on a motionless surface, as shown. If a force of 24 N is applied on the 4 kg block, then the contact force between A and B is

Three Blocks a, B and C

A) 6

B) 12

C) 24

D) 0

Answer: B

Explanation:

Three Blocks a, B and C

Acceleration of system

The contact forces between A and B is

= (

6. Which of the following velocity-time graphs shows a realistic situation for a body in motion

A)

Velocity-Time Graphs - A

B)

Velocity-Time Graphs - B

C)

Velocity-Time Graphs - C

D)

Velocity-Time Graphs - D

Answer: C

Explanation:

The slope of a velocity graph represents the acceleration of the object.

So, the value of the slope at a particular time represents the acceleration of the object at that instant.

Above graph shows the velocity-time graph for a body in motion for some time two velocity is practically not feasible as shown in option A, B, D so these options are incorrect.

7. A man walks on a straight road from his home to a market 3 km away with a speed of 6 km/h. Finding the market closed, he instantly turns and walks back home with a speed of 9 km/h. The average speed of the man over the interval of time 0 to 40 min. is equal to

A)

B) 5

C)

D) 6

Answer: A

Explanation

A man walks from his home to market with a speed of 6 km/h.

Distance = 3 km and time .

and he returns back with a speed of 9 km/h in rest of time of 10 minutes. Distance =

So, Average speed from 0 to 40 min =

8. The acceleration of a particle is increasing linearly with time t as The particle starts from the origin with an initial velocity u. The distance travelled by the particle in time t will be

A)

B)

C)

D)

Answer: C

Explanation:

At

We get,

v =

Again

On integrating both sides we get,

at t = 0; s = 0 and

At

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