PHY 121 Exam 2 (ch 6-9) Name - CPP

[Pages:2]PHY 121

Exam 2 (ch 6-9)

Name:

A 2.00 kg block, m2, slides with an initial speed up a ramp with initial speed of 4.00 m/s. The coef of friction is 0.500 and = 30?. The blocks come to rest after moving 3 meters.

a. Use kinematics/Newton's Laws to solve for m1.

vave = x / t ?(0+4) = 3 / t t = 1.5 sec

b. Use Energy conservation to solve for m1.

a = v / t a = 0-4 / 1.5 a = -2.67 m/s2

Ff = ? FNormal Ff = .5 2(g)cos30 Ff = 8.66 N

FNet

= mT a

m1g ? 2(g)sin30 ? Ff = (m1 + 2) -2.67

10m1 ? 10 ? 8.66 = -2.67m1 - 5.33

m1 = 1.05 kg

Block m2 rises a distance of h, where h = sin30? (3 meters) = 1.5 m

Einitial

- Ff d

K1 + K2

+ U1 + U2 - Ff d

?(m1+m2)v2 + m1 gh1 + 0 - Ff d

?(m1+2)42 + m1(10)3 ? 8.66 (3)

m1 = 1.05 kg

= Efinal

= K1f + K2f + U1f + U2f

= 0 + 0 + 0 + m2gh2f

=

2(10)1.5

A 40.0 kg skier encounters a dip in the path. The dip has a circular cross section with radius of 12.0 m. What is the normal force of the skier at point B, if the skier is traveling at a speed of 8.00 m/s at point A?

Einitial

= Efinal

K+ U

= Kf + Uf

?m v2 + m g h = ? m vf2 + 0

?40 82 + 40(10)1.75 = ?40 vf2

vf = 10 m/s

FN ? mg = m v2 / r FN ? 400 = 40 102 / 12 FN = 733 N

We included on the board during the exam that the skier increases speed as proceeding through the dip, should have added "at point A"

A 2.0 kg ball travels to the right and impacts with a 2nd stationary ball of mass 3.0 kg. After the impact, the 2nd ball travels to the right with a speed of 6.0 m/s and the 2.0 kg ball travels to the left with a kinetic energy of 1.0 Joules. What was the initial speed of the 2.0 kg ball?

mv + MV 2v + 0 v = 8 m/s

= m vf + M Vf = 2(-1) + 3(6)

Kf = ? m v2 1 = ? 2 (vf)2 vf = -1 m/s (to the left)

PHY 121

Exam 2 (ch 6-9)

Name:

A 1.0 kg ball travels to the right and impacts with a 2nd stationary ball of mass 4.0 kg. Following the

collision, the 2nd ball travels to the right with a speed of 6.0 m/s and the 1.0 kg travels to the left with a

Kinetic Energy of 2 Joules. What was the initial speed of the 1st ball?

mv + MV = m vf + M Vf

1v

= 1(-2) + 4(6)

v = 7

A 60.0 kg skier encounters a dip in the path. The dip has a circular cross section with radius of 10.0 m. What is the normal force of the skier at point B, if the skier is traveling at a speed of 12.00 m/s at point A?

A 3.00 kg block, m2, slides with an initial speed up a ramp with initial speed of 4.00 m/s. The coef of friction is 0.400 and = 30?. The blocks come to rest after moving 3 meters.

a. Use kinematics/Newton's Laws to solve for m1.

b. Use Energy conservation to solve for m1.

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