**Question 5: ****The
odometer of a car
reads 57321.0 km
when the clock shows
the time 08:30
AM. What is the
distance moved by
the car, if at 08:50
AM, the odometer
reading has changed
to 57336.0 km?
Calculate the speed
of the car in km/min
during this
time. Express the
speed in km/h also.**

**Answer: **Initial
reading of the
odometer of the car
= 57321.0 km

Final reading of the
odometer of the car
= 57336.0 km

Distance covered by
the car

= Final reading of
the odometer of the
car − Initial
reading of the
odometer of the car

= 57336.0 − 57321.0
= 15 km

The given car starts
at 8:30 a.m. and
stops at 8:50 a.m.

Therefore, time
taken by the car to
cover the distance
is (8:50 − 8:30) min
= 20 min

Distance covered by
the car = 15 km

Time taken by the
car = 20 min

Again,

60 min = 1 h

Time taken by the
car =

**Question 6: ****Salma
takes 15 minutes
from her house to
reach her
school on a
bicycle. If the
bicycle has a speed
of 2 m/s, calculate
the distance between
her house and the
school.**

**Answer: **Time
taken by Salma to
reach her school
from her home = 15
min = 15 × 60 = 900
s

Speed of her bicycle
= 2 m/s

Distance covered =
Speed × Time taken =
2 × 900 = 1800 m

1000 m = 1 km

**Question 7:****Show
the shape of the
distance-time graph
for the motion in
the following cases:**

(i) A
car moving
with a constant
speed.

(ii) A car parked on
a side road.

**Answer: **(i)A
car moving with a
constant speed
covers equal
distance in equal
intervals of time.

Such motion of car
is represented in
the given
distance-time graph.

(ii)The
distance-time graph
of a car parked on a
road side is such
that with the
increase in time,
there is no change
in distance, as
shown in the given
figure.

**Question 8: ****Which
of the following
relations is
correct?**

(i) Speed = Distance
× Time

**Answer:**(ii)
Speed of an object
is given by the
relation

**Question 9: ****The
basic unit of speed
is:**

(i) km/min

(ii) m/min

(iii) km/h

(iv) m/s

**Answer: **(iv)
m/s

The basic unit of
distance is metre
(m).

The basic unit of
time is second (s).

Therefore, the basic
unit of speed is
m/s.

**Question 10:****A
car moves
with a speed of 40
km/h for 15 minutes
and then with a
speed of 60 km/h**

for the next 15
minutes. The total
distance covered by
the car is:

(i) 100 km

(ii) 25 km

(iii) 15 km

(iv) 10 km

**Answer:**

(ii) 25 km

Case I

Speed of the car =
40 km/h

Time taken = 15 min
=

Distance covered, d1
= Speed × Time taken
= 40 × 0.25 = 10 km

Case II

Speed of the car =
60 km/h

Time taken = 15 min
=

Distance covered, d2
= Speed × Time taken
= 60 × 0.25 = 15 km

Total distance
covered by the car,
d = d1 + d2 = 10 +
15 = 25 km

Therefore, the total
distance covered by
the car is 25 km.

**Question
11: ****Suppose
the two photographs,
shown in Figure 1
and Figure 2, had
been taken at
an interval of 10
seconds. If a
distance of 100
metres is shown by 1
cm in
these photographs,
calculate the speed
of the blue car.**

Figure 1 Vehicles
moving in the same
direction of on a
road

Figure 2 Position of
vehicles shown in
Figure 1 after some
time

**Answer: **The
distance covered by
the blue car (as
evident from the
photograph) from one
white

strip to another,
which is measured by
scale is 1.4 cm.

It is given that 1
cm is equivalent to
100 m.

Therefore, 1.4 cm is
equivalent to 140 m.

Distance travelled
by the car = 140 m

Time interval
between the two
photographs = 10 s

**Question
12: ****Figure
shows the
distance-time graph
for the motion of
two vehicles A and
B. Which one of them
is moving faster?**

Distance-time graph
for the motion of
two cars

**Answer: **Vehicle
A is moving faster
than vehicle B.

Speed is given by
the relation

This relation shows
that speed of a
vehicle is greater
if it covers maximum
distance in a given
interval of time. To
compare the
distance, draw a
line perpendicular
to the timeaxis, as
shown in the
following
distance-time graph.

From the graph, it
is evident that for
a given time t, the
distance covered by
vehicle A is more
than vehicle B.
Hence, vehicle A is
moving faster than
vehicle B.

**Question
13: ****Which
of the following
distance-time graphs
shows a truck moving
with speed which
is not constant?**