121.

Two identical piano wires kept under the same tension T have a fundamental frequency of 600 Hz. The fractional increase in the tension of one of the wires which will lead to occurrence of 6 beats/s when both the wires oscillate together would be

• 0.02

• 0.03

• 0.04

• 0.04

A mass m moving horizontally (along the x -axis) with velocity v collides and sticks to mass of 3m moving vertically upward (along the y -axis) with velocity 2v. The final velocity of the combination

A block of mass m is in contact with the cart C as shown in the figure


The coefficient of static friction between the block and the cart is μ. The acceleration α of the cart that will prevent the block from falling satisfies

A ball moving with velocity 2 ms^-1 collides head on with another stationary ball of double the mass. If the coefficient of restitution is 0.5, then their velocities (in ms^-1) after collision will be

• 0,1

• 1,1

• 1,0.5

• 1,0.5

A man of 50 kg mass standing in a gravity free space at height of 10 m above the floor. He throws a stone of 0.5 kg mass downwards with a speed 2 ms^-1. When the stone reaches the floor, the distance of the man above the floor will be

• 9.9 m

• 10.1 

• 10 m

• 10 m

A student measures the distance traversed in free fall of a body, initially at rest in a given time. He uses this data to estimate g, the acceleration due to gravity. If the maximum percentage errors in measurement of the distance  and the time are e₁ and e₂ respectively, the percentage error in the estimation of g is

• e₁ - e₂

• e₁ + 2e₂

• e₁+ e₂

• e₁+ e₂

An explosion blows a rock into three parts. Two parts go off at right angles to each other. These two are 1 kg first part moving with a velocity of 12 ms^-1 and 2 kg second part moving with a velocity of 8 ms^-1.If the third part flies off with a velocity of 4 ms^-,its mass would be

• 5 kg 

• 7 kg

• 17 kg

• 17 kg

The mass of a lift is 2000 kg. When the tension in the supporting cable is 28000 N, then its acceleration is 

• 30 ms^-2 downward

• 4 ms^-2  upwards

•  4 ms^-2  downwards

•  4 ms^-2  downwards

A body under the action of a force, acquires an acceleration of 1 ms^-2. The mass of this body must be

• 

• 20 kg

• 10 kg

• 10 kg

A closed loop PQRS carrying a current is placed in a uniform magnetic field. If the magnetic forces on segments PS, SR and RQ are F₁, F₂ and F₃ respectively and are in the plane of the paper and along the directions shown, the force on the segment of QP is

• F₃ - F₁-F₂

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