What horizontally-applied force will accelerate a 400-kg crate at 1 m/s^2 across a factory room floor against a friction force of half its weight?

a) 600 n b) 1600 n c) 2000 n d) 2400 n e) none of the above

The position of a dragonfly that is flying parallel to the ground is given as a function of time by r⃗ =[2.90m+(0.0900m/s2)t2]i^− (0.0150m/s3)t3j^. a: at what value of t does the velocity vector of the insect make an angle of 34.0 degree clockwise from the x-axis? b: at the time calculated in part (a), what is the magnitude of the acceleration vector of the insect? c : at the time calculated in part (a), what is the direction of the acceleration vector of the insect?

Identical marbles are released from the same height on each of the following four frictionless ramps . compare the speed of the marbles at the end of each ramp. explain your reasoning

Can anybody me with this? ? (picture included.)