### Class XI

A stone of mass 0.25 kg tied to the end of a string is whirled round in a circle of radius 1.5 m with a speed of 40 rev./min in a horizontal plane. What is the maximum speed with which the stone can be whirled around if the string can withstand a maximum tension of 200 N?
1. 35 m s−1
2. 37 m s−1s−1 H
3. 33 m s−1
4. 33 m s
When an object undergoes acceleration
1. there is always an increase in its velocity
2. there is always an increase in its speed
3. a force always acting on it
4. all of the above
A man of mass 70 kg stands on a weighing scale in a lift which is moving upwards with a uniform speed of 10 m s−1s−1, what would be the reading on the scale?
1. 75 kg
2. 35 kg
3. 70 kg
4. 105 kg
A nucleus is at rest in the laboratory frame of reference. If it disintegrates into two smaller nuclei
1. the products must move in same direction.
2. the products must move at an angle in opposite directions.
3. the products must move in opposite directions.
4. the products must move at an angle in same direction.
A batsman deflects a ball by an angle of 45∘∘ without changing its initial speed which is equal to 54 km/h. What is the impulse imparted to the ball? (Mass of the ball is 0.15 kg.)
1. 4.6 kg m s−1
2. 4.2 kg m s−1
3. 4.4 kg m s−1
4. 4.8 kg m s−1
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