Anyone please send hard numerical type questions on motion physics class 9 more than 10! Plzz
Answers
Question 1
A train accelerates from 36 km/h to 54 km/h in 10 sec.
(i) Acceleration
(ii) The distance travelled by car.
Answer a. Acceleration is given by
a
=
Δ
v
Δ
t
Δ
v
=
54
−
36
=
18
k
m
/
h
r
=
5
m
/
s
So a=.5 m/s2
b. Distance is given by
S
=
u
t
+
1
2
a
t
2
Now u=36 km/hr =10m/s
s
=
10
×
10
+
1
2
×
.5
×
10
2
So s=125m
Question 2
A body whose speed is constant
(a) Must be accelerated
(b) Might be accelerated
(c) Has a constant velocity
(d) Cannot be accelerated.
Answer might be accelerated
Question 3
A truck travelling at 54 km/h is slow down to 36 km/h in 10 sec. Find the retardation
Answer Here u=54 km/h =15 m/s ,v=36 km/h=10 m/s
Acceleration is given by
a
=
Δ
v
Δ
t
a
=
10
−
15
10
=
−
.5
So a=-.5 m/s2
Negative sign implies retardation
Question 4
A particle is moving in a circle of diameter 20 m. What is its distance and as per the table given below
Rounds Displacement Distance
1
1.5
2
2.5 Answer After every round, particle comes to it starting position. So displacement at full rounds will be zero
Rounds Displacement Distance
1 0
20
π
1.5 20 m
30
π
2 0
40
π
2.5 20m
50
π
Question 5
A scooter travelling at 10 m/s speed up to 20 m/s in 4 sec. Find the acceleration of scooter.
Answer Acceleration is given by
a
=
Δ
v
Δ
t
a
=
20
−
10
4
=
10
4
=
2.5
So a=2.5 m/s2
Question 6
A train starts from rest and accelerate uniformly at the rate of 5 m/s2 for 5 sec. Calculate the velocity of train in 5 sec.
Answer Here u=0 ,a= 5m/s2 ,t= 5 sec,v=?
Now
v
=
u
+
a
t
v
=
0
+
5
×
5
=
25
m/s
Question 7
A object moves with uniform positive acceleration. Its velocity-time graph will be
(a) A straight line parallel to the time axis
(b) A straight line inclined at an obtuse angle to the time axis
(c) A straight line inclined at an acute angle to the time axis
(d) None of these.
Answer Answer is (c)
Question 8
The maximum speed of a train is 90 km/h. It takes 10 hours to cover a distance of 500 km. Find the ratio of its average speed to maximum speed?
Answer
Average speed
=
total distance
t
i
m
e
=
500
10
=
50
km/hr
Ratio of average speed to maximum speed= 50:90=5:9
Question 9
A car start from rest and acquire a velocity of 54 km/h in 2 sec. Find
(i) the acceleration
(ii) distance travelled by car assume motion of car is uniform?
Answer u=0, v=54 km/h=15 m/s ,t=2 sec
a) Acceleration is given by
a
=
Δ
v
Δ
t
a
=
15
−
0
2
So a=7.5 m/s2
b) Distance is given by
S
=
u
t
+
1
2
a
t
2
s
=
0
×
2
+
1
2
×
7.5
×
4
s=15m
Question 10
An object dropped from a cliff falls with a constant acceleration of 10 m/s2. Find its speed 5 s after it was dropped.
Answer
v
=
u
+
a
t
u
=
0
v
=
10
×
5
=
50
m
/
s
Question 11
A ball is thrown upwards and it goes to the height 100 m and comes down
1) What is the net displacement?
2) What is the net distance?
Answer As it comes down to the initial point
Net displacement is zero
Net distance=200 m
Practice questions on motion
Question 12
Two cars A and B race each other. The Car A ran for 2 minute at a speed of 7.5 km/h, slept for 56 minute and again ran for 2 minute at a speed of 7.5 km/h. find the average speed of the car A in the race.
Answer We know that
D
i
s
t
a
n
c
e
=
s
p
e
e
d
×
t
i
m
e
Distance travelled in first 2 minute =
7.5
×
2
60
= 0.25 km
Distance travelled in last 2 minute =
7.5
×
2
60
= 0.25 km
Total distance = .25+.25 = 0.5 km
Total time = 2+2+56 = 60 minute = 1 hr
Average speed = 0.5/1
= 0.5 km/hr
Question 13
Anand leaves his house at 8.30 A.M for his school. The school is 2 km away and classes start at 9.00 A.M. If he walks at a speed of 3 km/h for the first kilometre, at what speed should he walk the second kilometre to reach just in time?
Answer
s
p
e
e
d
=
d
i
s
t
a
n
c
e
t
i
m
e
or
t
i
m
e
=
d
i
s
t
a
n
c
e
s
p
e
e
d
For travelling 1 km with 3 km/hr,
Time taken = 1/3 hr = 20 min
Now he has to reach school in 30 min,So he has cover another 1 km in = 30 -20 =10 min= 1/6 hr
So speed should = distance /time= 1/(1/6) = 6 km/hr
Question 14
An object moves along a straight line with an acceleration of 2 m/s2. If its initial speed is 10 m/s, what will be its speed 2 s later?
Answer u=10 m/s,t=2 s, a=2 m/s2
v
=
u
+
a
t
v
=
10
+
2
×
2
=
14
m/s
Question 15
A bullet hits a Sand box with a velocity of 20 m/s and penetrates it up to a distance of 6 cm. Find the deceleration of the bullet in the sand box.
Answer 3333.3 m/s2
Question 16
A particle experiences constant acceleration for 20 seconds after starting from rest. If it travels a distance D1 in the first 10 seconds and distance D2 in the next 10 seconds then,
(a) D2 = D1
(b) D2 = 2D1
(c) D2 = 3D1
(d) D2 = 4D1
Answer (c)
Question 17
The velocity -time graph of SUV is given below. The mass of the SUV is 1000 kg.
Numerical Questions and answers on Motion for Class 9 physics
a. What is the distance travelled by the SUV is first 2 seconds?
b. What is the braking force at the end of 5 seconds to bring the SUV to a stop within one seconds?
Answer a. The distance travelled by the SUV is first 2 seconds = Area of
Δ
A
B
E
=
1
2
×
A
E
×
B
E
=
1
2
×
2
×
15
=
15
m
b. Acceleration will be given by the slope of the line CD
a
=
0
−
15
6
−
5
=
−
15
m
/
s
2
Now mass of the SUV =1000 Kg
Braking Force will be
F
=
m
a
=
1000
×
−
15
=
−
15000
N
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