# Physics Quiz for SSC CGL 2018 : Pinnacle Coaching Center

# Physics Quiz for SSC CGL 2018 : Pinnacle Coaching Center

Physics Quiz for SSC CGL 2018 : Pinnacle Coaching Center

**Motion in a Plane**

**Q1. When a body moves with a constant speed along a circle**

(a) its velocity remains constant

(b) no force act on it

(c) no work is done on it

(d) no acceleration is produced in it

**Q2. Which of the following is not a vector quantity?**

(a) speed

(b) velocity

(c) torque

(d) displacement

**Q3. In uniform circular motion**

(a) both velocity and acceleration are constant

(b) acceleration and speed are constant but velocity changes

(c) both acceleration and velocity changes

(d) both acceleration and speed are constant

**Q4. A body is revolving with a constant speed along a circle. If its direction of motion is reversed but the speed remains the same, then**

(a) the centripetal force will not suffer any change in magnitude

(b) the centripetal force will have its direction reversed

(c) the centripetal force will suffer any change in direction

(d) the centripetal force would be doubled

**Q5. When a body moves with a constant speed along a circle**

(a) no work is done on it

(b) no acceleration is produced in the body

(c) no force act on the body

(d) its velocity remains constant

**Q6. A body is travelling in a circle with constant speed. It **

(a) has a constant velocity

(b) is not accelerated

(c) has an inward radial acceleration

(d) has an outward radial acceleration

**Q7. When a particle is in uniform circular motion it does not have**

(a) radial velocity and radial acceleration

(b) radial velocity and tangential acceleration

(c) tangential velocity and radial acceleration

(d) tangential velocity and transverse acceleration

**Q8. A body is moving with a constant speed v in a circle of radius r. its angular acceleration is**

(a) vr

(b) v/r

(c) zero

(d) vr^{2}

**Q9. What happens to a centripetal acceleration of a revolving body if you double the orbital speed v and halves the angular velocity ****ω ?**

(a) the centripetal acceleration remains unchanged

(b) the centripetal acceleration is halved

(c) the centripetal acceleration is doubled

(d) the centripetal acceleration quadrupled

**Q10. A stone of mass m is tied to a string of length l and rotated to a circle with a constant speed v if the string is released the stone flies**

(a) radially outward

(b) radially inward

(c) tangentially outward

(d) with an acceleration mv^{2}/l

**Q11. If a particle moves in circle describing equal angles in equal interval of times, its velocity vector**

(a) remains constant

(b) change in magnitude

(c) changes in direction

(d) changes both in magnitude and direction

**Q12. In the projectile motion, if air resistance is ignored, the horizontal motion is at**

(a) constant acceleration

(b) constant velocity

(c) variable acceleration

(d) constant retardiation

**Q13. A stone is just released from the window of a moving train along a horizontal straight track. The stone will hit the ground following a**

(a) straight line path

(b) circular path

(c) parabolic path

(d) hyperbolic p[ath

**Q14. A bullet is dropped from same height when another bullet is fired horizontally. They will hit the ground**

(a) one after the other

(b) simultaneously

(c) depends on observer

(d) none of the above

**Q15. Two bullets are fired horizontally with different velocities from the same height. Which will reach the ground first?**

(a) slower one

(b) faster one

(c) both will reach simultaneously

(d) it cannot be predicted

##### Explanation:

**Ans 1. (c)** On circular motion, the force acts along the radius and displacement at a location is perpendicular to the radius i.e., θ =90°

As work done = FS cos 90°=0

**Ans 2. (a)** A vector quantity has both magnitude and direction. In the given options, speed has only magnitude; therefore, it is non vector or scalar quantity.

**Ans 3. (c)** in the circular motion with constant speed, acceleration is always inward, its magnitude is constant but direction changes hence acceleration changes so does velocity K.E. is constant.

**Ans 4.(a)** A body is revolving with a constant speed along a circle. If its direction of motion is reversed but the speed remains the same, then the centripetal force will not suffer any change in magnitude.

**Ans 5.(a)** Body moves with constant speed, it means that it perform uniform circular motion. In this motion the direction of motion is always perpendicular to centripetal force. Hence the work done by centripetal force is always zero.

**Ans 6. (c)** body moves with constant speed it means that tangential acceleration =0 and only centripetal acceleration exists whose direction is always towards the center or inward.

**Ans 7.(c)** It has only tangential velocity and radial acceleration or centripetal acceleration.

**Ans 8.(c)** Since the circular motion is uniform, therefore there is no change of angular velocity. Thus angular acceleration is zero.

**Ans 9.(a)** Since centripetal acceleration

a_{C}= v^{2}/r=rω^{2}=vω because v=rω

so there is no change if we double v and halve ω

**Ans 10.(c)** In uniform circular motion, the body move with tangential velocity (v_{T}) and a_{C}. if a_{C}=0 then it implies that the body is no longer bound to rotate in circle and so no change in the direction of velocity. Hence it move tangentially to the circle outward with velocity v_{T}.

**Ans 11. (c)** Since velocity is defined as v= ∆s/∆t=r ∆θ/∆t where s= P_{1} P_{2}=r.θ, is an arc to circle, which is swept by the particle in ∆t time , r is radius of circle which is constant in uniform circular motion and θ is angular displacement in ∆t time.

Hence if particle is a circle describe equal angles in equal intervals of time, its speed remains same but the direction changes due to centripetal acceleration a_{C.}

**Ans 12.(b)** If air resistance is ignored then there is no acceleration in horizontal direction in the projectile motion. Hence the particle moves with constant velocity in horizontal direction.

**Ans 13.(c)** The horizontal velocity of the stone will be the same as that of the train. In this way the horizontal motion will be uniform. The vertical motion will be controlled by the force of gravity. Hence it is accelerated motion. The resultant motion is a parabolic trajectory.

**Ans 14.(b)** In both the cases the initial velocity in the vertical downward direction is zero. S they will hit the ground simultaneously.

**Ans 15.(c)** The time taken to reach the ground depends on the height from which the projectile is fired horizontally. Here height is same for both the bullets and hence they will reach the ground simultaneously.

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