Category: General Physics
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What is the Final Speed?
A man standing on very slick ice fires a rifle horizontally. The mass of the man together with the rifle is 70 kg, and the mass of the bullet is 10 g. If the bullet leaves the muzzle at a speed of 500 m/s, what is the final speed of the man? Known variables: (man) mass(m1): 70 kg (bullet)mass(m2): 10…
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What is the Mass of Water Collected?
A 5000 kg open train car is rolling on frictionless rails at 22.0 m/s when it starts pouring rain. A few minutes later, the car’s speed is 20.0m/s. What mass of water has collected in the car? Known Variables: Mass of train (m1) = 5000 kg v1 = 22 m/s v2 = 20 m/s Conservation of momentum: Pi – Pf = 0…
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What is the Speed of the Ball?
A 71 kg baseball player jumps straight up to catch a line drive. If the 140 g ball is moving horizontally at 29 m/s, and the catch is made when the ballplayer is at the highest point of his leap, what is his speed immediately after stopping the ball? Known variables: (player) m1= 71 kg (ball) m2 = 140 g or .140 kg…
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How much Torque?
How much torque must the pin exert to keep the rod in the figure from rotating? Calculate this torque about an axis that passes through the point where the pin enters the rod and is perpendicular to the plane of the figure. Known Variables: L: 80 cm or .8m M(of the rod)= 2.0 kg m(of the weight)= 500g or .5 kg…
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Magnitude of the Vertical Force
A 57 kg diver stands at the end of a 29 kg springboard, as shown in the figure. The board is attached to a hinge at the left end but simply rests on the right support. What is the magnitude of the vertical force exerted by the hinge on the board? Known Variables: (diver)m1 = 57 kg (springboard)m2= 29 kg…
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Horizontal Force
You want to slowly push a stiff board across a 20 cm gap between two tabletops that are at the same height. If you apply only a horizontal force, how long must the board be so that it doesn’t tilt down into the gap before reaching the other side? This is a conceptual problem. The board needs…
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Spring Constant
Experiments using “optical tweezers” measure the elasticity of individual DNA molecules. For small enough changes in length, the elasticity has the same form as that of a spring. A DNA molecule is anchored at one end, then a force of 1.5 nN (1.5 x 10-9 N) pulls on the other end, causing the molecule to stretch by 5.0…
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What is the Value of the Spring Constant?
You need to make a spring scale to measure the mass of objects hung from it. You want each 1.5cm length along the scale to correspond to a mass difference of 0.10 kg. What should be the value of the spring constant? Known In a spring scale: F = mg = kx Solve for k: k = mg/x…
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Force to be Motionless in Position
A man is attempting to raise a 7.5 m-long, 35 kg flagpole that has a hinge at the base by pulling on a rope attached to the top of the pole, as shown in the figure below. With what force does the man have to pull on the rope to hold the pole motionless in this position? The…