Question

If retardation produced by air resistance of projectile is one-tenth of acceleration due to gravity, the time to reach maximum height

A. decreases by 11 percent
B. increases by 11 percent
C. decreases by 9 percent  
D. increases by 9 percent
Answer :   decreases by 9 percent
Solution :
The time to reach the maximum height without air resistance; $${t_1} = \frac{u}{g} = \frac{u}{{10}},$$
and with air resistance, $${t_2} = \frac{u}{{10 + 1}} = \frac{u}{{11}}$$
$$\eqalign{ & = \frac{{{t_1} - {t_2}}}{{{t_1}}} \times 100 = \left[ {\frac{{\frac{u}{{10}} - \frac{u}{{11}}}}{{\frac{u}{{10}}}}} \right] \times 100 \cr & = 9\% \left( {{\text{decreases}}} \right) \cr} $$

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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