Physics Questions & Answers - Free Online Practice

611.

A body is projected with an initial velocity u at angle $\theta$ to the horizontal. If $R_{max}$ is the maximum range of the projectile, what does the relation $\frac{u^{2}}{R_{max}}$ represent?

The vertical distance covered

Acceleration due to gravity

The horizontal distance covered

The acceleration of the body

View answer & explanation

Correct answer is B

$R_{max} = \frac{u^{2}}{g}$

Hence, $g = \frac{u^{2}}{R_{max}}$

612.

Which of the following quantities are dimensionally independent?

I. Dielectric constant II. Momentum III. Efficiency IV. Refractive index

I and II

II, III and IV

I, II, III and IV

I, III and IV

View answer & explanation

Correct answer is D

The quantities Efficiency, Dielectric constant and Refractive index are dimensionless.

613.

A block is acted upon by TWO horizontal forces as illustrated in the diagram above. The block accelerates at 1.5 $ms^{-2}$ . Calculate the mass of the block.

6kg

9kg

10kg

15kg

View answer & explanation

Correct answer is A

Total force exerted on the block = (10 - 1)N =9N

Force = mass x acceleration

9 = m x 1.5

m = 9/1.5 = 6kg

614.

A body of mass m moving around a circle of radius r with a uniform speed v experiences a centripetal force F. The work done by the centripetal force on it is

zero

Fmr

$\frac{Fr}{m}$

View answer & explanation

Correct answer is B

Work is done whenever the given conditions are satisfied. (ii) there is a displacement of the body caused by the applied force along the direction of the applied force. No displacement takes place in this case. So, work done by a centripetal force is always zero.

The work done by centripetal force in the case of a uniform circular motion is 0 joules.

615.

A dam is able to hold a large quantity of water because its wall is

thickest at the top

thickest at the middle

thickest at the bottom

of the same thickness throughout

View answer & explanation

Correct answer is C

The pressure of the water is much greater deeper down and the dam needs to be thick at the bottom so that it is strong enough to withstand this larger pressure