Question

1. An object starts with an initial velocity of 10 m s -
and acceleration 5 m s? Find the distance covered
by it in 5 s.
2. A bus running at a speed of 18 km h-' is stopped in
2.5 s by applying brakes. Calculate the retardation
produced
3. A bullet initially moving with a velocity of 20 m s-1
strikes a target and comes to rest after penetrating a
distance of 10 cm in the target. Calculate the retardation
caused by the target.
4. The average time taken by a person to react to an emergency
is one-fifteenth of a second and is called the reaction
time'. If a bus is moving with a velocity of 60 km h-
and its driver sees a child moving across the road, how
much distance would the bus had moved before he could
press the brakes? The reaction time of the people increases
when they are intoxicated. How much distance had the
bus moved if the reaction time of the driver were 0.5 s
under the influence of alcohol ?​

Answer 1

ANSWER- 1

u=10m/s,a=5m/s

2

,t=5s

S=ut+

2

1

at

2

S=10×5+

2

1

×5×5

2

S=112.5m

ANSWER-2

Initial velocity = 18 km/h = 18×5/18 m/sec

= 5 m/sec

[ km/h = 5/18 m/sec ]

final velocity = zero

acceleration = change in velocity/time

= ( final velocity - intial velocity)/time

= ( 0 - 5)/2.5 = -2 m/s²

so, retardation = 2m/s²

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