IMO 2010 QUESTION NO. 9

An object of mass 20 kg moves along a straight line on a smooth horizontal surface. A force F acts on the object in its direction of motion.A graph of force against time is shown here. What is the velocity of the object at t=6s if its velocity at t=4s is 4 m/s?

An object of mass 20 kg moves along a straight line on a smooth horizontal surface. A force F acts on the object in its direction of motion.A graph of force against time is shown here. What is the velocity of the object at t=6s if its velocity at t=4s is 4 m/s? 
my options are a) 3.5 m/s b)4.5 m/s c)5.3 m./s d)6.2 m/s

Solution

For the first 3 seconds, the force is 20 N. For the last 3 seconds, the force decreases from 20 N to 0 N. To determine the velocity at 3 seconds, use the following equation. 

Average force * time = mass * increase of velocity 
The average force at first 3 second is 20N and at 2nd 3 second is 10N

Momentum =Forcextime=massxchange in velocity

20 * 3 = 20 * ∆v 
∆v = 3 m/s 

To determine the increase of velocity for the last 3 seconds, use the same equation. In this case the average force is 10 N. 

10 * 3 = 20 * ∆v 
∆v = 1.5 m/s 
The final velocity is equal to the sum of these two numbers. 
Final velocity = 4.5 m/s(Answer)

Question 49 -17TH NSO B

A man of mass 55Kg climbs up a flight of steps to reach the spring board .The spring is 6m above the water surface

a small block B of mass 1kg is placed on a block A of mass 5kg as shown in figure.A constant force of 10N is applied on block A.If all the surfaces are assumed frictionless and block B is at the right end of block A ,then the time in which block B separates from A is

NSO 2013 B QUESTION NO 17

NSO 2013 A QUESTION 3

NSO-2013 SCIENCE SECTION B-Q1

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