Some important Results
1) The three equation of motion are
* v= u + at
** S= ut + (at²/2.
*** v²- u²= 2aS.
2) When a body starts from rest its initial velocity is taken as zero i.,e., u= 0
3) When a body comes to rest its final velocity is taken as zero i.,e., v= 0
4) If a body is slowing down with time then its acceleration is taken as negative.
5) When a body falls freely its initial velocity is taken as u= 0 and g= 9.8 m/s².
2) A constant retarding force of 50N is applied to a body of mass 20kg moving initially with a speed of m/s. How long does the body take to stop? 6s
3) What constant force is needed to stop a bullet of mass 25g in a distance of 10cm if the bullet has speed of 300 m/s. 1.125 x 10⁴N
4) A train moving with a velocity of 20 m/s is brought to rest by applying brakes in 5 second. Find the retarding force acting on it if the mass of the train is 1000 tonne? -4 x 10⁶N
5) A ball of mass 0.1 kg hits the hands of a player with a velocity of 20 m/s is brought to rest 0.01 second. Find the retarding force applied by the hand of the player? -200N
6) How much momentum will a dumbbell of mass 10kg transfer to the floor, if it falls from a height of 0.8m? Take acceleration due to gravity as 10m/s². 40NS
7) Find the force required to stop a car of mass 1000 kg and a loaded truck of mass 10000 kg in 2 seconds, if they are moving with some velocity of 5 m/s. -25000 N
8) A cricket ball of mass 70g, moving with a velocity of 0.5m/s is stopped by a player in 0.5 s. What is the force applied by the player to stop the ball ? -0.07 N
9) A car of mass 1000kg moving with a velocity of 45km/h collides with a tree and comes to rest in 5s. What will be the, force exerted by the car on the tree? 2500N
10) A truck starts from rest and roll down a hill with constant acceleration. It travels a distance of 400 metres in 20s. Find its acceleration. Find the force acting on it, if its mass is 7 metric tonnes. 2m/s², 14000 N
11) A bullet of mass 5g travelling at a speed of 120 m/s penetrates deeply into a fixed target and is brought to rest in 0.01s. find
a) the distance of penetration in the target. 0.6 m
b) the average force exerted on the bullet. 60N
12) What is the weight of a body of mass 12kg? What is the force acting on it? 120N, 120N
13) Find the force required to produce an acceleration of 5 m/s² in a mass of 5000 gram. 25N
14) A force of 500 dyne acts on a body of mass 0.04 kg over a distance of 100m. Find the final velocity and time for which force will act when the mass initially is at rest. 500 cm/s, 40s
15) Find the force required to produce an acceleration of mass 10 m/s² on a body of mass 8kg in
a) dyne. 80 x 10⁵ dyne
b) newton. 80N
16) How much force will be needed to increase the velocity of a body of mass 10kg from 20m/s² to 100 m/s² in 40 seconds. 20N
17) An object of mass 40 kg is acted upon by a constant retarding force of 400N. If it were initially moving with a speed of 300 m/s, in how much time will it come to rest. 15s
18) A body of mass 100g is resting on a frictionless surface. Find the distance covered by it in 200 seconds when acted upon by a force of 0.4 N. 80km
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