Physics Exam 1

a) 55kg b) 50kg c)47.5kg Hints: a) Fn-mg=ma => Fn=m(a+g) where a = 1 550N/10=55kg b) Fn-mg=ma => Fn=m(a+g) where a = 0 500N/10=50kg c) Fn-mg=ma => Fn=m(a+g) where a = 0.5 475N/10=47.5kg

5. A man is in an elevator. He has a mass of 50 kg, and so of course when stationary the bathroom scale reads 50 kg. What does it read if a) If the elevator is starting from the bottom and accelerates up uniformly from 0 to 2 m/s in 2 seconds? b) If the elevator goes at a constant 2 m/s c) If the elevator slows down as it reaches the top, and goes from 2 m/s to 0 in 4 seconds. Assume g = 10 m/s2 for simplicity

a) a=1.333m/s/s b) 17.4N a) mg-uMg=Ma+ma mg-uMg=a(M+m) a = (mg-uMg)/(M+m) a=1.33 b) mg-T=ma T=mg-ma T=m(g-a) T=2(10-1.333) = 17.4N

A block of mass M = 4 kg is placed on a table, and the coefficient of kinetic friction is μk = 0.3. (Assume that it is already in motion) It is pulled along by a string, that goes over a pulley, and a mass is placed at the end of the pulley. If the hanging mass is m = 2 kg, what is the acceleration of the block? If the hanging mass, m, is replaced by a force F, what value of F is required to get the same acceleration?

a) 2m/s/s b) 16N (I think) a) Mg-mg = Ma + ma => a=2 b) T-mg=ma or Mg-T=Ma

A block of mass M= 3kg has a string attached, it goes over a pulley and a block of mass m=2 kg is hung from it. What is a) the acceleration, and b) the Tension. Assume no friction

a) 320m Hint: solve for t using delta y. delta y = -50. Then, use delta x formula. Multiply t by initial velocity of 100.

A helicopter is on a humanitarian mission and is to deliver food packages to a small village. The helicopter flies 50 m above ground with a constant speed of 100 m/s. How far from the target does the pilot need to drop the package so that it hits the target spot?

a) 4000N |f| = F = 0.2FN = 0.2 x 2000 x 10 = 4000 N

A team of reindeer pull a sleigh of mass 2000 kg over snow, with a constant speed of 5m/s. If the coefficient of kinetic friction is μk = 0.2, what force do they need to pull with?

10.3 Hint: Set y1 and y2 equal, y2's t is (t-1). Solve for t. To find where, plug t into one equation

A ttime t=0 seconds, a man throws a ball straight up with a speed of 15 m/s. One second later, he throws a second ball straight up, also with a speed of 15 m/s. How far off the ground are they (in meters) when they collide?

a) 67m/s Hint: Solve for t using delta y. Delta y = -100. Find magnitude of Vx (50) and Vy (44). Find Vy by using v=Vo+at

An airplane is flying, horizontally, at a uniform velocity of v = 50 m/s at a height of 100 meters above the ground. It drops an aid package to the ground below. What is the speed of the package when it hits the ground? (Answer in m/s and assume no air resistance).

When: 2.5s Where: 18.75m Hint: Set y1 and y2 equal, y2's t is (t-1). Solve for t. To find where, plug t into one equation

At t=0, you throw a ball up with v=20 m/s. A second later, (i.e. at t=1 s), you throw another ball up with 20 m/s. Where do they collide? Let g = 10 m/s^2

260 m/s/s Hint: Plug into second derivative

The position of a body moving on straight line is given by the equation: x(t)= -10 - 5t2 + 15t3 Find the acceleration at t=3 s x is given in meters, t in seconds

a) 2m/s^2 Vf^2 - Vo^2 = 2ax solve for a x = 900 Vf = 0 Vo = 60 (because 100 - 40 )

When a high-speed passenger train traveling at 100 m/s rounds a bend, the engineer is shocked to see that a locomotive has improperly entered the track from a siding and is at a distance D=900 meters ahead. The locomotive is moving at 40 m/s. The engineer of the highspeed train immediately applies the brakes. What is the magnitude of the passenger trains acceleration if a collision is to be just avoided?

a) x = 33.3m Hint: v^2-Vo^2 = 2ax Find acceleration using F=ma, a=F/m F=uFn so a=(umg)/m a = -6 plug back into first equation to get 33.3

You are driving at 20 m/s. In an emergency, you hit the brakes (hard!) and skid to a halt. If the coefficient of kinetic friction is μk = 0.6, how far do you travel before coming to a stop?

11.8 m/s Hint: Find hypotenuse for distance, find times and add times. Distance over time.

You move 500 m north at 10 m/s, followed by 1200 m west at 20 m/s. What, in m/s, is the magnitude of your average velocity?

a) 6 m/s b) 2 m/s Hint: Speed is total distance over total time, velocity is delta distance over total time

You run 100 meters in 12 seconds, turn around and jog back half-way in a further 13 seconds. What is a) Average speed b) Average velocity (take initial direction to be positive)