1. What is the acceleration for a car that goes from 45 km/hr to 80 km/hr in 3.0

Question

1. What is the acceleration for a car that goes from 45 km/hr to 80 km/hr in 3.00 sec? (Points: 6)
1.8 m/s2
3.0 m/s2
3.2 m/s2
3.5 m/s2

3. Suppose that while walking in a straight line at a uniform speed, you throw a ball straight up about 2 or 3 m without breaking stride. Where will it land? (Points: 6)
Behind you
In front of you
Right back in your hand
To the right of you

4. A projectile is fired over level ground with an initial vertical velocity of 20 m/s and an initial horizontal velocity of 30 m/s. Using g = 10 m/s2, the distance from the launching to the landing points is: (Points: 6)
40 m
60 m
80 m
120 m

5. A 120-kg box is on the verge of slipping down an inclined plane with static coefficient of friction 0.90. What is the angle of inclination of the plane? (Points: 6)
34o
42o
47o
56o

7. If the kinetic energy of a football player running at 8.1 m/s is 3610 J, what is the mass of that player? (Points: 6)
110 kg
125 kg
135 kg
155 kg

ANY will help please!!!

Explanation / Answer

1) The acceleration a = (final speed - initial speed)/time a = (22.22 m/s-12.5 m/s) / 3 s a = 3.2 m/s2 3) The ball will land right back into the hand 4) The distance from the launching to landing point is R = u^2 sin2(theta)/2g u is the initial speed = sqrt(400 + 900) = 36.05 m/s the angle of projection is theta = tan^-1(3/2) = 56.31 R = 1300*sin112.62/20 = 120 m 5) The angle of inclination is theta = tan^-1(mu) mu is the coefficient of static friction theta = tan^-1(0.9) theta = 41.98 = 42 degree(appx) 7) Mass of the player is m = 2KE/v^2 m = 2*3610/8.1^2 m = 110 kg

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