IX physics assignment term-1:-
Q1. A ball starts from rest and rolls down 20 metre down an inclined plane in 4 second.
(a) what is the acceleration of the ball?
(b) what is the velocity of the ball at the bottom of the inclined plane?
Q2. (a) why do you fall in the forward direction when a moving bus brakes to stop and fall backward when it accelerates from rest?
(b) car travels at a speed of 40 kilometre per hour for 2 hours and then 60 kilometre per hour for 3 hours. What is the average speed of the car during the entire journey?
Answers
Q.1
(a)
accleration=2.5 m/s^2
(b)v =10 m/s
Q.2
(a)due to the inertia.
(b)avg. v = 52 km /hr
Working out:
(I) The ball is said to roll from an inclined plane and we are given the value of the quantities related to its motion. Here, we can use the three equations of motion:
- v = u + at
- s = ut + 1/2 at²
- v² = u² + 2as
Here, symbols have their usual meaning. So, let's solve this question by putting the values.
(a) Given:
- u = 0
- s = 20 m
- t = 4s
To FinD:
- a = ?
By using 2nd equation of motion,
Acceleration of the ball = 2.5 m/s² towards the end.
(b) Given:
- u = 0 m/s
- a = 2.5 m/s²
- t = 4s
To FinD:
- v = ?
By using 1st equation of motion,
Velocity of the ball at the bottom = 10 m/s
━━━━━━━━━━━
(II) a) This phenomenon can be explained by the phenomenon of Inertia which is the tendency of a body to resists its state of rest or motion.
- When we are inside a bust at rest, our body is also at rest. When the body start acclerating, the lower body also moves with the bus but the upper body will try to maintain the state of rest for that instant. Hence we fall backwards, in order to maintain Inertia of rest.
- When we inside a moving bus, our body is also at motion. When the bus comes to rest suddenly, our upper body tries to maintain its Inertia of motion. Hence, we fall forward.
b) Here, we are given with two different speeds the car travels with but for two different time intervals:
- With speed 40 km/hr for 2 hours.
- With speed 60 km/hr for 3 hours.
For finding average speed, we need to find total distance and total time because Average speed = Total Distance / Total time.
- And, Distance travelled (1st) = 40 km/hr × 2 hrs
- Distance travelled (2nd) = 60 km/hr × 3 hrs
Total distance = Sum of the two intervals.
Because, Distance = Speed × Time.
Finding Average speed of the car,
Thus, the average speed of the car is 52 km/hr
And, we're done with all the answers !!
━━━━━━━━━━━━━━━━━━━━