Question 1 A ball is thrown straight up with a speed of 30 m/s. How high will it

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Question 1 A ball is thrown straight up with a speed of 30 m/s. How high will it be above its initial height after 2.5 s? Question 2 A 20 gram bullet is moving at a speed of 140 m/s when it strikes a large block of wood and lodges 3.0 cm into the wood. What is the magnitude of the average force decelerating the bullet during this event? Question 3 A wheel with rotational inertia of 2.0 kg?m2 is spinning at a rate of 3.0 rev/s. What average torque would be required to stop this wheel in at time of 10.0 s? Question 4 A balloon holds 240 m3 of helium. ?air = 1.29 kg/m3 ?He = 0.197 kg/m3 What is the maximum weight (empty balloon + cargo) that the balloon can lift? Question 5 A 2.0-kg mass moves with a speed of 5.0 m/s. It collides head-on with a 3.0 kg mass at rest. If the collision is perfectly inelastic, what is the speed of the masses after the collision?

Explanation / Answer

1)

A)S= ut-0.5gt^2

S= 30*2.5 ) -(0.5*9.8*2.5^2) = 44.375 m high

B)V^2 -u^2 = 2aS

we have final velocity = v=0

Initial velocity = u = 140 m/s

0-140^2 = 2*a*0.03

a= -326666.667 m/s^2

magnitude of the average force decelerating the bullet during this even = ma = 0.02*326666.667 = 6533.33 N

C)

angular decleration required =alpha = 3*2*pi/10 = 1.88 rad/s^2

torque = I*alpha = 1.88*2 = 3.77 Nm

D)

volume of He = 240 m^3

so buoyancy force =volume displaced*density of air = 240*1.29 = 309.6 kg

weight of ballon = 240*0.197 = 47.28 Kg

weight that the balloon can lift = 309.6-47.28 = 262.32 Kg

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