19 their connection with space and time properties

Didactic material #1

Didactic material #2

Q1.      For the two physical quantities, impulse and force, which one of the following is correct?

A            Impulse is a scalar and force is a scalar.

B             Impulse is a scalar and force is a vector.

C             Impulse is a vector and force is a scalar.

D             impulse is a vector and force is a vector.

(Total 1 mark)

Q2.

A force, F, varies with time, t, as shown by the graph and is applied to a body initially at rest on a smooth surface. Whatisthemomentumofthebodyafter 5.0 s?

A            zero.

B             12.5 N s.

C             25 N s.

D             50 N s.

(Total 1 mark)

Q3.        A particle of mass m strikes a rigid wall perpendicularly from the left with velocity v.

If the collision is perfectly elastic, the change in momentum of the particle which occurs as a result of the collision is

A            2mvtotheright.

B             2mvtotheleft.

C             mvtotheleft.

D             zero.

(Total 1 mark)

Q4.      The graph shows how the force acting on a body changes with time.

The body has a mass of 0.25 kg and is initially at rest. What is the speed of the body after 40 s assuming no other forces are acting?

A            200 ms^–1

B              400 ms^–1

C             800 ms^–1

D             1600 ms^–1

(Total 1 mark)

Q5. The graph shows how the resultant force applied to an object of mass 2.0 kg, initially at rest,varies with time.

What is the speed of the object after 1.0 s?

A            2.5 ms^–1

B             5.0 ms^–1

C             7.5 ms^–1

D             10 ms^–1

(Total 1 mark)

Q6. A rail truck X travels along a level track and collides with a stationary truck Y. The twotrucks move together at the same velocity after the collision.

Which line, A to D, in the table states how the total momentum and the total kinetic energy of the trucks change as a result of the impact.

(Total 1 mark)

Q7. A golf club undergoes aninelasticcollision with a stationary golf ball and gives it an initialvelocity of 60 m s^–1. The ball is in contact with the club for 15 ms and the mass of the ball is 4.5 × 10^–2 kg.

(a)          Explain what is meant by an inelastic collision.

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(1)

(b)         Calculate

(i)          the change in momentum of the ball,

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(ii)        the average force the club exerts on the ball.

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(4) (Total 5 marks)

Q8. In a football match, a player kicks a stationary football of mass 0.44 kg and gives it a speedof 32 m s^–1.

(a)          (i)    Calculate the change of momentum of the football.

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(ii)        The contact time between the football and the footballer’s boot was 9.2 m s. Calculate the average force of impact on the football.

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(b)         A video recording showed that the toe of the boot was moving on a circular arc of radius 0.62 m centred on the knee joint when the football was struck. The force of the impact  slowed the boot down from a speed of 24 m s^–1 to a speed of 15 m s^–1.

Figure 1

(i)          Calculate the deceleration of the boot along the line of the impact force when it struck the football.

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(ii)        Calculate the centripetal acceleration of the boot just before impact.

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(iii)             Discuss briefly the radial force on the knee joint before impact and during the impact.

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(4) (Total 7 marks)

Q9. A car travelling at 30 m s^–1 collides with a wall. The driver, wearing a seatbelt, is brought to rest in 0.070 s.

The driver has a mass of 50kg. Calculate the momentum of the driver before the crash.

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Momentum = .........................................................

(2)

Calculate the average resultant force exerted on the driver during impact.

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Average resultant force = .......................................

(3)

Explain why the resultant force is not the same as the force exerted on the driver by the seatbelt.

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