Question

A man throws balls with same speed vertically upwards one after the other at an interval of $$2\,\sec .$$  What should be the speed of throw so that more than two balls are in air at anytime?

A. Only with speed $$19.6\,m/s$$
B. More than $$19.6\,m/s$$  
C. At least $$9.8\,m/s$$
D. Any speed less then $$19.6\,m/s.$$
Answer :   More than $$19.6\,m/s$$
Solution :
Height attained by balls in $$2\,\sec $$  is $$ = \frac{1}{2} \times 9.8 \times 4 = 19.6\,m$$
the same distance will be covered in 2 second (for descent)
Time interval of throwing balls, remaining same. So, for two balls remaining in air, the time of ascent or descent must be greater than 2 seconds. Hence speed of balls must be greater than $$19.6\,m/\sec .$$

Releted MCQ Question on
Basic Physics >> Kinematics

Releted Question 1

A river is flowing from west to east at a speed of $$5$$ metres per minute. A man on the south bank of the river, capable of swimming at $$10$$ metres per minute in still water, wants to swim across the river in the shortest time. He should swim in a direction-

A. Due north
B. $${30^ \circ }$$ East of north
C. $${30^ \circ }$$ West of north
D. $${60^ \circ }$$ East of north
Releted Question 2

A boat which has a speed of $$5 km/hr$$   in still water crosses a river of width $$1 \,km$$  along the shortest possible path in $$15 \,minutes.$$   The velocity of the river water in $$km/hr$$  is-

A. 1
B. 3
C. 4
D. $$\sqrt {41} $$
Releted Question 3

In $$1.0\,s,$$  a particle goes from point $$A$$  to point $$B,$$  moving in a semicircle of radius $$1.0 \,m$$  (see Figure). The magnitude of the average velocity-
Kinematics mcq question image

A. $$3.14 \,m/s$$
B. $$2.0 \,m/s$$
C. $$1.0 \,m/s$$
D. Zero
Releted Question 4

A ball is dropped vertically from a height $$d$$ above the ground. It hits the ground and bounces up vertically to a height $$\frac{d}{2}.$$  Neglecting subsequent motion and air resistance, its velocity $$v$$  varies with the height $$h$$  above the ground as-

A. Kinematics mcq option image
B. Kinematics mcq option image
C. Kinematics mcq option image
D. Kinematics mcq option image

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